# Headlights still dim



## CodyD (Apr 5, 2021)

So I have a 2004 Silverado 1500 with 2 Rockford fosgate p3-12s running of a Rockford fosgate t1500bdcp ran a test tone to set my gain I know it’s not perfect but it’s around 1200 watts of power at 2ohms have a 320 amp high output alternator brand new agm battery big 3 upgrade done with 4/0 cause that’s all I had and my headlights still dim any ideas????


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## ckirocz28 (Nov 29, 2017)

CodyD said:


> So I have a 2004 Silverado 1500 with 2 Rockford fosgate p3-12s running of a Rockford fosgate t1500bdcp ran a test tone to set my gain I know it’s not perfect but it’s around 1200 watts of power at 2ohms have a 320 amp high output alternator brand new agm battery big 3 upgrade done with 4/0 cause that’s all I had and my headlights still dim any ideas????


1200 watts really shouldn't dim your lights, upgrade that power wire to 1/0, and the alternator charge wire and your grounds. A 320 amp alternator could REALLY use some 1/0 wire.


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## CodyD (Apr 5, 2021)

ckirocz28 said:


> 1200 watts really shouldn't dim your lights, upgrade that power wire to 1/0, and the alternator charge wire and your grounds. A 320 amp alternator could REALLY use some 1/0 wire.


Well 4/0 is bigger then 1/0 and all my wires are 4/0 with exception to the wire that goes from my battery to my amplifier. I understand that 1200 watts shouldn’t dim my headlights the problem is that it does.


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## Holmz (Jul 12, 2017)

It is possible that the alternator may not respond fast enough during those thumps?

Capacitor threads have abounded as of late, maybe search for supercaps or ultracaps over the last month?

Whether that is what you need or not, probably requires an oscilloscope, or a try it and see approach.


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## skydeaner (Mar 25, 2006)

Solid amp too so likely not a shortage of capacitance for the amp power supply section. Test resistance from batt to amp terminal? From ground terminal to neg battery post? Anything weird going on? Is this while idling? That 320 drops to at least 220 at idle. Never seen one that didn't lose a minimum of that much. 

If all else fails you can get led headlights and forget about it lol. Since they are current based devices instead of voltage based it would take a vdrop below their minimum voltage rating to cause a dimming. And this is a pretty broad range since also usually use pretty sophisticated (if you get decent ones) step-up power supplies to reach about 20-30v in the first place.


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## daloudin (Nov 2, 2020)

Check for voltage drop at the alternator terminal - you may need to get your regulator or diodes checked out.

Sent from my SM-G965U using Tapatalk


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## gghouck (Mar 25, 2021)

CodyD said:


> Well 4/0 is bigger then 1/0 and all my wires are 4/0 with exception to the wire that goes from my battery to my amplifier. I understand that 1200 watts shouldn’t dim my headlights the problem is that it does.


What size is the battery to amp cable?


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## CodyD (Apr 5, 2021)

My voltage dropped to almost 12 at idle, that is extremely low for the amount of watts I’m using and power I have to give, could it be maby a bad ground at my amplifier?


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## CodyD (Apr 5, 2021)

And the alternator is brand new just installed it yesterday


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## doeboy (May 2, 2012)

What is the brand of alternator? I agree to check resistance of the grounds. What is the idle rpm? You won't get anywhere near 320 at idle. If it is a reputable vendor they may be able to tell you what to expect at idle.


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## CodyD (Apr 5, 2021)

It’s a Mechman it’s 220 at idle still well more then I need


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## daloudin (Nov 2, 2020)

CodyD said:


> My voltage dropped to almost 12 at idle, that is extremely low for the amount of watts I’m using and power I have to give, could it be maby a bad ground at my amplifier?


If it's dropping to 12 at the alternator at idle then you've got something wrong with the voltage regulator. Contact Mechman and explain. 

Measure your alternator chassis to ground to make sure that path is good. 

If that voltage drop is at the amp but it's not dropping at the alternator then its a wiring problem. All grounds should measure a dead short in continuity meter and down to milliohms almost instantly on resistance. 

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## ckirocz28 (Nov 29, 2017)

CodyD said:


> Well 4/0 is bigger then 1/0 and all my wires are 4/0 with exception to the wire that goes from my battery to my amplifier. I understand that 1200 watts shouldn’t dim my headlights the problem is that it does.


I assumed that 4/0 was a typo and you meant 4 gauge, never seen any 4/0.


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## daloudin (Nov 2, 2020)

ckirocz28 said:


> I assumed that 4/0 was a typo and you meant 4 gauge, never seen any 4/0.


You can use 4/0 but you generally have to use adapters on each end unless your running some surfboard amps. You should try working with 750MCM sometime. 

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## CodyD (Apr 5, 2021)

4/0 is just all I had, I’m an electrician so iv got a lot of wire on hand, had 4/0 welding wire so that’s what I used, that’s only for my big 3 the wire from my battery to my amplifier if 1/0 so I didn’t have to do the adapter thing for my amp


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