# capacitor for my head unit



## Ludemandan (Jul 13, 2005)

I have an intermittent problem where my ignition switch momentarily loses contact when I turn off the car, causing the head unit to turn off and restart. It's pretty annoying when I want to turn off the car and continue listening to music. Instead of replacing the switch, I thought of putting a 12v capacitor across the ignition and ground wires of the deck to supply it with the momentary charge necessary to keep it on. What size/type of cap would I need to make this work?

Dan


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## chad (Jun 30, 2005)

It SHOULD NOT take much as that's just a low current trigger, you may have to experiment, go 16V or higher.

Only problem is that the cap is going to be supplying current for everything else that runs off of the acc feed, you may need to implement a diode to keep the cap from back-feeding into the rest of the electrical system for that instant. I had a ham radio that used to keep my head unit powered up for a while when the key was turned off due to it's internal cap.


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## Ludemandan (Jul 13, 2005)

Keeping the other components on might be good too. My Helix amp does a 3-4 second fault check routine whenever it turns on, but since the deck takes at least that long I don't know if that's happening too. So I'd need a cap capable of holding the signal to my entire system momentarily. 

I know there are different types of capacitors, but I don't know enough about electronics to go to a store and buy one based only on the voltage. There's polar, non-polar, etc... Any tips?


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## chad (Jun 30, 2005)

You want polar but again, I have NO idea how big, it depends on current draw of that trigger. In newer headunits the red wire is now just a voltage trigger like a remote turn on, it does not draw much current at all. UNLIKE the old days when the red drew current and the yellow (constant on) was there just to retain memory settings/clock. 

Again you may need a diode to keep it from backfeeding to everything else on that ACC circuit. 

So from the car.... Diode in series with switched power (observe polarity) then CAP positive. ground the cap neg. You could always go larger on a cap and use a bleeder resistor to make an RC timer.


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## Ludemandan (Jul 13, 2005)

Cool, thanks. Now it's time to experiment!


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## DirtyDog (Jul 30, 2009)

Let us know what the results are when finalized. i was thinking ofdoing the same thing. When i have my key turned back and start my truck up, the radio resets everything and the Avic takes 1min to boot up everything...sucks....


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## IBcivic (Jan 6, 2009)

just a suggestion, why not just wire in an ''off delay'' timer. my pontiac had one from the factory, so the h-u could play for 5 mins after the ignition was turned off or if i put it in ''acc'' it would play 'til the battery went flat.

edit> the pac tr-7 can be easily set up to do this.


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## TrickyRicky (Apr 5, 2009)

I think you have the HU wired wrong. The constant power wire should be hooked to a wire that has 12V or so all the time. Then there the remote power wire that goes to your ignition (dont get this confused with the blue remote wire, that one is for your accessories) switch. You might want to check that out first, because it doesnt make any sense that your HU resets everytime you turn off/on the car. 

HU dont need capacitors. Although there are a few HU that require a 10gauge wire from the battery to the HU, but never a capacitor. 

Everyone keeps believe the hype of the capacitor. How everyone says a capacitor is a good way to get rid off the light dimming but it aint. If your lights are dimming that means you need to upgrade your battery and alternator.


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## ChrisB (Jul 3, 2008)

Jeanious2009 said:


> I think you have the HU wired wrong. The constant power wire should be hooked to a wire that has 12V or so all the time. Then there the remote power wire that goes to your ignition (dont get this confused with the blue remote wire, that one is for your accessories) switch. You might want to check that out first, because it doesnt make any sense that your HU resets everytime you turn off/on the car.
> 
> HU dont need capacitors. Although there are a few HU that require a 10gauge wire from the battery to the HU, but never a capacitor.
> 
> Everyone keeps believe the hype of the capacitor. How everyone says a capacitor is a good way to get rid off the light dimming but it aint. If your lights are dimming that means you need to upgrade your battery and alternator.


I bet those headlights won't dim as bad if one installs the capacitor right next to them.


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## sqshoestring (Jun 19, 2007)

I ran a 1f cap on a PS and it would run the HU for something like 5 seconds IIRC. I'd say pick one up cheap (I paid $15 shipped for mine on epay) and put a diode on there to run the HU. But, sure I would investigate a timed relay to run it and see what was cheaper, the cap would be harder to install for a HU.

In fact you can make a timer relay yourself with a little figuring I'm sure someone on the net has. Run a small cap on the relay trigger with a diode and a resistor that bleeds current off IIRC I forget, anyway that is how amps delay turn on and things like that. Turn it on and cap fills instantly and relay turns on. When you turn it off the cap only has to power the relay trigger until it is empty or the resistor on it bleeds current to ground low enough to shut it down (that is how you adjust delay, or change cap size). Power the HU from the relay.

Here is boughten one: AGASTAT 12 Volt On-Delay Off-Delay Time Delay Relay SST12QEA

If it times both on and off, just put a normal relay with it to turn on instant and it will still turn off on delay. There may be others I did just a quick search.


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## IBcivic (Jan 6, 2009)

one member even had a bunch of cheap 15$ turbo timers for sale a while back


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## TrickyRicky (Apr 5, 2009)

ChrisB said:


> I bet those headlights won't dim as bad if one installs the capacitor right next to them.


Yeah put one capacitor on each headlight, that should do it, lolepper:.

If you cant find the wire inside your dash that has a constant 12v, just do what I would do, run a wire from the battery to your HU, problem solved. And the wire doesnt have to be 10gauge, unless asked by the manufacture or model. As far as for the ignition switch wire on you HU (which really acts like a remote wire), if you cant find that either, rigg it up, buy a cheap toggle switch and wire that to the ignition wire. It should add point for looks as many people that get in your car is going to be asking "What is that switch for", and you can always say "dont touch that switch, it turns on the NOS".:laugh:


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## Ludemandan (Jul 13, 2005)

Jeanious2009 said:


> I think you have the HU wired wrong. The constant power wire should be hooked to a wire that has 12V or so all the time. Then there the remote power wire that goes to your ignition (dont get this confused with the blue remote wire, that one is for your accessories) switch. You might want to check that out first, because it doesnt make any sense that your HU resets everytime you turn off/on the car.
> 
> HU dont need capacitors. Although there are a few HU that require a 10gauge wire from the battery to the HU, but never a capacitor.
> 
> Everyone keeps believe the hype of the capacitor. How everyone says a capacitor is a good way to get rid off the light dimming but it aint. If your lights are dimming that means you need to upgrade your battery and alternator.


I don't have the HU wired wrong. It loses power when the ignition switch (which I replaced a while ago) momentarily loses all contact as I turn off the car, which is sometimes. If I put the exact right pressure on the key as I turn the car off, the HU stays on. The problem is with the ignition switch, and I'm trying to mask it. I'm not trying to boost my HU, or solve light dimming or whatever it is people normally do with capacitors. Refer to my original post.

DirtyDog - I'll definitely post back with the results!


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## TrickyRicky (Apr 5, 2009)

Ludemandan said:


> I don't have the HU wired wrong. It loses power when the ignition switch (which I replaced a while ago) momentarily loses all contact as I turn off the car, which is sometimes. If I put the exact right pressure on the key as I turn the car off, the HU stays on. The problem is with the ignition switch, and I'm trying to mask it. I'm not trying to boost my HU, or solve light dimming or whatever it is people normally do with capacitors. Refer to my original post.
> 
> DirtyDog - I'll definitely post back with the results!


Yeah I would fix the switch first and if no luck then go with plan B. Oh as for capacitors, trust me their worthless. Some caps can sell for up to 400.00 and suckers actually buy them, instead of buying a 250.00 hi-output alternator and a 200.00 battery.


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## sam3535 (Jan 21, 2007)

Jeanious2009 said:


> Yeah I would fix the switch first and if no luck then go with plan B. Oh as for capacitors, trust me their worthless. Some caps can sell for up to 400.00 and suckers actually buy them, instead of buying a 250.00 hi-output alternator and a 200.00 battery.


Read his posts; he wasn't looking for a cap for that. Caps (for head units) can have very positive benefits such as smoothing out ripple and providing a constant 12v level.


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## benny (Apr 7, 2008)

sam3535 said:


> Read his posts; he wasn't looking for a cap for that. Caps (for head units) can have very positive benefits such as smoothing out ripple and providing a constant 12v level.


That's why he calls himself "Jeanius"


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## sam3535 (Jan 21, 2007)

benny said:


> That's why he calls himself "Jeanius"


Kind of like that genious beer?

brilliant


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## IBcivic (Jan 6, 2009)

it seems the original issue has been forgotten....he is looking for a way to be able to switch the ignition from run to acc. w/o having his h-u turning off and having to wait for a re-boot of his entire system. a capacitor on the h-u turn-on wire would probably help. he never mentioned that he was looking to stabilize the h-unit's overall power feed.

whenever the word ''capacitor'' is mentioned on diyma, it turns out to be a ''vultures on fresh roadkill'' party


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## sqshoestring (Jun 19, 2007)

I told you a cheap cap for amps will work, just bulky and you would need a diode behind it (that cost about nothing). I've done it on my 12v supply in the house hundreds of times. In fact with the volume down I have a smaller cap on there that is .3f or something and it will stay on a few seconds with that. Now you can get the super caps that are small, but I don't recall cost on those.

If I have the volume up the HU runs a set of 6x9, it will kill it pretty fast, however if you are saying it is less than half a second or so it may not take much cap to do it....and your HU is running amps not speakers.

Actually if that hot wire that runs the HU does not run a bunch of other stuff, you may not need a diode. The cap will power anything on that circuit without a diode.


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## chad (Jun 30, 2005)

Dude, the lead he is putting a cap on is a voltage sense line, VERY little current draw, a big cap will leave it on for hours.


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## sqshoestring (Jun 19, 2007)

chad said:


> Dude, the lead he is putting a cap on is a voltage sense line, VERY little current draw, a big cap will leave it on for hours.


You sure? My HUs still shut down and "reboot" if the normal power is cut. Still have the downtime I assume this is about? This 880prs certainly takes longer to get started up as well, though not that long. Odds are a timer would be better here anyway, IMHO.


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## IBcivic (Jan 6, 2009)

2 options... a diode[check valve] in series with a cap of'' X''uf[need to experiment] or any off delay timer that works on 12v. the pac tr7 can do alot more than by-pass the alpine dvd safeties...it's programable. i use it to trigger my diy trunk release using the oem 2 button remote.


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## chad (Jun 30, 2005)

I fail to see how this is so difficult for some.

It's JUST like an amplifier, you have a constant source of power, this now, in modern headunits is the brunt of the current draw, the current draw of the red (switched wire) is Nil, just like your remote turn on on the amplifier. A smallish cap can and will do the trick, nobody think farads, it will never shut off. This is why I mentioned days ago that you may have to make an RC network by adding a bleeder resistor to set the timing.


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## sqshoestring (Jun 19, 2007)

chad said:


> I fail to see how this is so difficult for some.
> 
> It's JUST like an amplifier, you have a constant source of power, this now, in modern headunits is the brunt of the current draw, the current draw of the red (switched wire) is Nil, just like your remote turn on on the amplifier. A smallish cap can and will do the trick, nobody think farads, it will never shut off. This is why I mentioned days ago that you may have to make an RC network by adding a bleeder resistor to set the timing.


That could be, I have no idea what his HU pulls. If remote it will not take much.


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## Ludemandan (Jul 13, 2005)

Yes, it is a remote-turn on to a deadhead. Eclipse 7200 MKII.

Edit: Actually, I just remembered, all my stuff is turned on by a relay (yeah, it's been a while since I worked on my system). If I recall, those Tyco relays require a full 12v to switch. If you put any type of load in series with the relay coil - such as another relay or a remote terminal - it will not switch on with 13.5v. Since a relay is not sensitive equipment, there's no harm in using a capacitor with a voltage rating slightly higher than the charging voltage. That's what I'll try.


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## sqshoestring (Jun 19, 2007)

Most amps use 16v caps on the supply side.


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## circa40 (Jan 20, 2008)

I have no idea if this is what you're looking for. But a few years ago I built a mini capacitor bank using a few capacitor leftovers. I bought a mini PCB and project box from Radioshack and soldered six 5600uf 16v caps in parallel (33600uf total). 

The purpose of the cap bank was to give me a few minutes of storage when I disconnected the battery (I hate resetting all my presets) and use it as a filter and power stabilizer with some added capacitance.

Edit: I wired it to the constant 12v power supply wire for my HU.


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## Ludemandan (Jul 13, 2005)

Sweet. How long did the supply last?


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## circa40 (Jan 20, 2008)

Ludemandan said:


> Sweet. How long did the supply last?


hummm, good question....It was enough time for me to replace a battery...I would guess 5 mins? You can always up the capacitance if you need a longer down time. 

But it sounds like you probably dont need much.


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## chad (Jun 30, 2005)

If you put that cap bank on his switched 12V wire it will power the damn headunit for hours..... Again, the simple little cap in a CB RADIO FRONT END triggered my headunit in my truck for about 3 seconds, no diode either to keep it from feeding back.

PEOPLE PLEASE read what he wants to do and understand ow these headunits are working, there's a damn good reason the "red wire" no longer has a fuse in it


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## Ludemandan (Jul 13, 2005)

circa40 said:


> hummm, good question....It was enough time for me to replace a battery...I would guess 5 mins? You can always up the capacitance if you need a longer down time.
> 
> But it sounds like you probably dont need much.


Since I can see how much capacitance that bank has from the photos, I can get some kind of reading on how much I might need... 5600 uF x 6 = 33600 uF. Five minutes divided by 1/4 second (estimated time of non-contact) is 1200. 33600/1200=28. So I could round up and get a cap 50 uF and it might work. Pretty rough calc, but it's a place to start.


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## sqshoestring (Jun 19, 2007)

I did a test for you, I have an ancient cap out of a computer printer or whatever it was. Its 40v 78000uf and near the size of a 1f cap. I turned on my test HU running a pair of 6x9, turned the volume down to zero, and shut off the 13.8v PS. At 2 seconds the lights went out. I don't remember what caps are in the PS from when I rebuilt it (old pyramid 10A) but nothing stays on with it alone when you hit the switch. Then I added my 1f cap to it and tried the same thing again. It ran for 14 seconds. Now given the HU may run to 10v or something, all the voltage lights went out on the 1f cap a few seconds before it died but I don't know what they are set to.


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## chad (Jun 30, 2005)

did you apply a constant 12V to the ''yellow wire'' and the cap to the ''red wire''?

NOT tying the red and yellow together?


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## Ludemandan (Jul 13, 2005)

Thanks for doing that bit of field research! I realized that there's a difference between the deck staying on and just holding its settings (while off), so circa40's experience may not apply. I'm assuming your 1 farad cap is charged to 13.8v. 1,000,000 uF/14 seconds is 71,400 uF/second, so assuming I need to hold it on for 1/4 second, I need a 17,800 uF capacitor. So I could get a couple of these: 
NTE NEV10000M16HI 10,000uF CAPACITOR 16 VDC

I also realized I only need to hold the deck on, not a relay. The deck controls the relay. Again, it's been a while since I tore into this.


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## circa40 (Jan 20, 2008)

Have you checked Mouser Electronics - Electronic Component Distributor or DigiKey Corp. | Electronic Components Distributor | United States Home Page

I've great success buying from both companies.


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## sqshoestring (Jun 19, 2007)

chad said:


> did you apply a constant 12V to the ''yellow wire'' and the cap to the ''red wire''?
> 
> NOT tying the red and yellow together?


No that is running both wires, the entire HU with no sound to guesstimate RCA output only. The 1f test was with both caps, the 78K cap is back behind the PS I didn't want to dig it out. Its on there for fun or to help keep power clean, I never really tested it just wanted to use it for something.

Yes mouser is a good place though I think digikey dropped their minimum order last time I ordered there. Sometimes someone like MCM has something cheap too.

Here is a cheap 33K at mouser UFW1C333MRD $5.57.
Could spring for one of these with screw terminals 36DA273F025AB2A $11.60
Just a quick search.


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## chad (Jun 30, 2005)

But see, the constant IS NOT losing power, the switched trigger (which draws VERY LITTLE current) DOES lose power. powering the headunit fully from the cap is a completely invalid test in the OP's application..... Why did you test this? I think people are completely confusing 3 threads that are going on at the same time, the OP does not want/need filtering for the constant, this is not the goal.

Again he needs just enough to hold the trigger high for a second or two, that's it, no more, a large cap will keep it on too long.


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## BoostedNihilist (Mar 3, 2008)

you can easily see what chad is saying is true simply by looking at the gauge of the yellow wire and comparing that to the gauge of the red wire. 

I would use a switch.


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## jon_k (Sep 16, 2009)

ChrisB said:


> I bet those headlights won't dim as bad if one installs the capacitor right next to them.


Doesn't matter without a diode, the capacitor becomes part of the electrical system. The capacitor will try to supply ANYTHING that needs power when the system isn't delivering regardless of cap placement.


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## chad (Jun 30, 2005)

jon_k said:


> Doesn't matter without a diode, the capacitor becomes part of the electrical system. The capacitor will try to supply ANYTHING that needs power when the system isn't delivering regardless of cap placement.


Mother of god, get in the car, lets go on a crusade! :laugh:

You mean that all this time that everyone thinking that the amplifier wire coming from the battery to the trunk is a diode was actually wrong? and that nothing else will see or use that cap?

Yer allright man, people are gonna argue with you, just grin and bear it.


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## sqshoestring (Jun 19, 2007)

chad said:


> But see, the constant IS NOT losing power, the switched trigger (which draws VERY LITTLE current) DOES lose power. powering the headunit fully from the cap is a completely invalid test in the OP's application..... Why did you test this? I think people are completely confusing 3 threads that are going on at the same time, the OP does not want/need filtering for the constant, this is not the goal.
> 
> Again he needs just enough to hold the trigger high for a second or two, that's it, no more, a large cap will keep it on too long.


This is the DQ forum, I don't really know what wires are losing power.

Anyway if it is the red wire I tested that. All I had handy was a 1K uf 35v and it ran it for about 2 seconds, but sometimes more or less it seemed. So I tried the 78K uf 40v and it ran it for 2:50 playing music the whole time. That is 459uf/sec if I did my math right.

So I'll put my guess in at 1500-2000 uf for a few seconds, since I doubt you will care if it stays on longer. Or buy two 1K uf and use one or both depending. Hey next time I am into my car maybe I will add one that would be nice to have 5 seconds or so. I don't think the amp remote (unhooked on this HU test) has anything to do with the red wire's current, but don't know. Also don't know if anything else runs on the car's wire to the HU, that could pull it down faster.


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## BoostedNihilist (Mar 3, 2008)

umm, the ignition wire is losing power?

If you tied the red and yellow wire together, and wired them to a cap that skews your results. He needs the cap to keep the red wire energized while his key hits the pickups in the ignition switch.

If you tied the red and yellow wires together your cap is powering the high current demand yellow wire, and the low current demand red wire. The red wire (in this guys situation) is the only wire which needs to be capped because the yellow wire is powered from a different source (a constant versus switched source). With both wires tied together your cap is seeing an unrealistic amount of current draw, and will discharge quicker. If you wired the cap to the red wire alone it would probably stay on for longer.

The talk of a remote wire is confusion. I think (if I remember correctly) the amp has a transistor used to turn the power supply on.. I think the parallel being made here is instead of the red wire carrying current to power the finals and whatnot the red wire now goes to a transistor which triggers the heavy current load onto the yellow wire for powering the finals, drive, whatnot. So, other than the fact that by powering the red wire with a cap and keeping the deck on, thereby keeping the remote wire to the amps on, they really have nothing to do with each other other than a comparison for logics sake.


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## sqshoestring (Jun 19, 2007)

I know all that, apparently I missed the part where he said only the red wire is losing power. Now I have tested it both ways for him; both wires and only the red wire.


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## Ludemandan (Jul 13, 2005)

I went out and bought a cap (why order one online?). This is the closest thing they had to what (I think) I need. They had nothing in lower voltage or higher capacitance. 










Will install soon and update thread with results.


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## BoostedNihilist (Mar 3, 2008)

> I know all that, apparently I missed the part where he said only the red wire is losing power. Now I have tested it both ways for him; both wires and only the red wire.


OP didn't out and out say that.. but , thinking cap /on, the constant isn't wired into the iggy switch


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## chad (Jun 30, 2005)

Take a chicken breast, thawed.

Preheat the grill

Put it on, in a bit sprinkle some natures on it and a bit of lemon.

In a bit

Put butter on it, not cheap ass ****... BUTTER.... roll it over, 

FRESH CRUSHED garlic on the other side and a BIT of butter...... 

Cook till done, eat.


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## chad (Jun 30, 2005)

Who wants to talk about killing the chicken?


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## Ludemandan (Jul 13, 2005)

Actually, hold on a second. I tore out my center console and thought about connecting this cap from acc to ground, and realized that it might constitute a short circuit for long enough to blow a fuse. That is, if it has low enough charging resistance. What do you guys think?


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## Ludemandan (Jul 13, 2005)

Success! It works exactly as planned. I've turned the key on and off over and over again with no interruption in the music. The deck still turns off immediately when I turn the acc off. It's no cure for the deck losing power when I start the car, but maybe that's a project for another day.


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## chad (Jun 30, 2005)

I ****ing toldja  Now, add a diode, 1n 4001....


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## chad (Jun 30, 2005)

Ludemandan said:


> *I have an intermittent problem where my ignition switch momentarily loses contact when I turn off the car, causing the head unit to turn off and restart. It's pretty annoying when I want to turn off the car and continue listening to music*. Instead of replacing the switch, I thought of putting a 12v capacitor across the ignition and ground wires of the deck to supply it with the momentary charge necessary to keep it on. What size/type of cap would I need to make this work?
> 
> Dan





sqshoestring said:


> I know all that, apparently I missed the part where he said


*WHERE HE SAID WHAT?*


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## chad (Jun 30, 2005)

....


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## BoostedNihilist (Mar 3, 2008)

> Success! It works exactly as planned. I've turned the key on and off over and over again with no interruption in the music. The deck still turns off immediately when I turn the acc off. It's no cure for the deck losing power when I start the car, but maybe that's a project for another day.


Wire your deck into the IGNITION 1 Wire and it won't turn off when cranking


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## Ludemandan (Jul 13, 2005)

Ignition 1? I only have one ignition wire.


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## sqshoestring (Jun 19, 2007)

Jeanious2009 said:


> I think you have the HU wired wrong. The constant power wire should be hooked to a wire that has 12V or so all the time. Then there the remote power wire that goes to your ignition (dont get this confused with the blue remote wire, that one is for your accessories) switch. You might want to check that out first, because it doesnt make any sense that your HU* resets* everytime you turn off/on the car.


This person posted this because the OP said "restart" which to some of us is what a HU does when you cut *all *the power to it, it resets. Though the OP did say "restart", it is not that clear so this threw me off as well.

After the OP said:


> I also realized I only need to hold the deck on, not a relay. The deck controls the relay. Again, it's been a while since I tore into this.


And while Chad was correct, now we know the OP maybe does not have a different issue. I posted that I tested *all *power wires on the HU on the cap, and when I had time I tested just the* one wire *and posted again with results for the one wire. What else do you want me to do? I took the time to help by testing and again when the issue was more clear to me. Glad the cap worked, problem solved.


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## BoostedNihilist (Mar 3, 2008)

Ignition 1 is the wire that stays on during crank. It stays on to power the computer, fuel pump, coils etc. Other 'ignition' items, such as your stereo, are cut out to provide the maximum current available to actually crank the engine. You can find ignition 1 on your ignition switch. You can tap into it, it is usually fairly heavy gauge. On some modern vehicles, the wires to the switch are VERY tiny, if you find the wires and they are tiny, don't tap into them.


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