headlights dimming , cap on

A friend just bought a new truck; its a 2008 chevy silverado crew cab. Of course all new toys need more base and so weve installed a small system that sounds good; but somehow are still running into the general problem of his headlights dimming. The system is extremely basic and simple: 2ea Kicker CVT 12s, Power Acoustik BAMF 1800/2, 5 farad PA CAP in an aftermarket box fitted for the truck. I have done basic car audio before and am an electrican by trade, so figured it would be easy but am now baffeled and need assitance. Speakers are 400w RMS & 800w peak, so the amp is more than enough for them. Wiring was kept seperate, 1 speaker per channel, and the cap is mounted right in front of amp so wires are as short as possible. The base control knob that came with the amp doesnt seem to work so we just took it out of the system. And the third problem is the that the amp stays on constantly. After we shut the truck off, it will recharge back to around 14v but it stays lit up and we assume that its drainging off the battery. Any help with these problems would be greatly appreciated.

I didn't even read it. You wanna know why? Because a CAP IS NOT YOUR ANSWER! Period. Went to BestBuy, huh?

You need a high output alternator. End of story. Start lookin'.

Move the cap to the headlights instead.


Otherwise there are lot of other threads about bigger alternators, second batteries, Big-3, low resistance cabling etc.
And even about using $20 batteries instead of 5F & 8F caps.

lose the cap. upgrade the battery under the hood. if the amp is staying on then you have the remote wire hooked to a constant 12v source so what did you hook it to? make sure all of your ground wires are as short as possible, screwed tightly to bare metal with all paint and primer sanded off. a seat belt bolt is not a good ground. make sure the wire is appropriately sized for the current draw of the amp, at least a true 4 gauge.

if after all of this the lights still dim, then i would chalk it up to it being a chevy truck because chevys have the most garbage electrical system out of any vehicle that i usually work on.

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Hey SnS - The Chevy LUV was ok!
LOL - A former soldier "talked" to me about driving a Jap car. He had a "Chevy" LUV!


rscwboy - keep in mind that the battery type & size remote from the surging amp has little effect unless extreme cables are used.
That's why an additional (AGM) battery is collocated with the amp.

Those that have a remote battery are conned into buying caps to compensate, but even then, a small AGM instead is better (ie, is smaller than the cap, is cheaper, and lasts far longer).

Extra batteries are not to make up for undersized alternator. An undersized alternator not only means battery flattening, but usually 2 Volts LESS to the amplifier (eg - 14.4V vs 12.4V - not that that should make a difference!)

what is a chevy LUV? light utility vehicle?

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I h8 u SnS - it took me decades to figure that out!!!

Yes - a rebadged Isuzu from early 1970s onwards. Often wins engine blow-up competitions (valve bounce, no oil or coolant).
It was the ute (pick-up) version of the Isuzu "Florian" - later Aska, SAAB etc with offshoots (like the 117 coupe). The LUV became the KB-series and then Rodeo.

People here pay a fortune for them because they think they are "Chevrolet". Blame GM for that!

hahaha, awesome. good info.

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You have the amp's remote terminal connected to a constant 12 volt source.  You should be able to find a switched power source to turn the amp on only when the Ignition is powered up.  Check the fuse in the top right corner of the fusebox that is located on the left end of the dash.   This information may or may not be for the 2008 model.  You will need to check it.

rscwboy, if you have gotten this far, I'd like to apologize for... well... SOME of our responses, especially the jabs (and there might be another here...), were you to have taken any of our responses as such...

Anyway. You really need to ditch the cap, and address the failure of your electrical system. ALL of the electrical power for a car (when running) comes from the alternator; thus my reference to "the failure". If your alternator is too small (potentially indicated by dimming lights, as in your particular case), this is a sure sign you need a larger one. OEM is undersized almost from the factory, let alone adding an additional 150A load from an "amp".

Yep... I already KNEW is was an E-swooswoo, but here's a little more info, re: Chevy LUV...

To echo soundnsecurity, ALL of the Chevy electrical systems are complete and total garbage. A 200,000 mile motor (OK, a 100,000 mile motor) with a 25,000 mile/three year alternator (or a 35,000 mile tranny (check the forums...), whichever comes first - YMMV - :P). Seriously, ANYTHING you can do to beef the overall system, you will be MILES ahead. This includes AFTERMARKET (as in NOT OEM) high output alternator, all new wires, and a better battery. Wax all of the underhood stuff, and re-wire it properly.

Cool - I'll refer future Isuzu questions to you Haemo.
"I
suzu who?" asked the Hummer driver... (LOL)   

rscwboy - being an electo you should understand the same 2 basic principles - source voltage, and distribution drop.
The peak vs RMS - notice the 2:1 ratio - ie, √2 x √2 = 2; so that's a non-issue.

The dc cap is equivalent to a PLC (esp ferro-resonant).
But a battery to a cap is like rotating machine (ac alternator) to a PLC.

The car alternator is the ac power station. If it is undersized, sags & brownouts occur.
But if it is big enough, the load can still dip due to other nearby loads etc - hence the PLC etc - or in the dc case - a battery or cap.

Granted, vehicle audio does not have transmission length as an issue, but the V=IR dips still occur.

If it is (say) a 1,000W input amp, a 120A alternator will certainly cover that. Maybe too an 80A depending on volume and other loads.
It's not a big sound system.

I'd suspect the distribution - especially grounding.
The cap cannot charge to 14V on just a battery unless the battery has been overcharged or has amazing surface charge!
(Typical batteries charged at 14.4V almost instantaneously drop to ~13.8V and eventually to a fully charged voltage of between 12.8 & 12.6V. (The battery capacity above ~12.8 is "surface charge".)

^^ what he said ^^

As an electrician, (I was a SeaBee electrician in the Navy for six years, as well) you should understand that nothing you put on the INSIDE of your electrical panel (or in the case of your car, the fusebox) can make you get any more power out of the grid! (In the case of your car again, the alternator)

Address the power source.

ok first, im a smartass by trade and at heart so not scaired away by others, like the fun.  second, im a pet monkey...meant to say that the cap stays on constantly. we cheated and the amp remote wire is on powered after you turn truck to start, doesnt even work in acc. checked with a load light and none of the fuses in the cab were switched off, all were constant??? not a "bestbuy" system so to say, similar idea though.  cap was used bc of the idea of a cap is to store energy until needed, during bass. seems to work for that process but its acting as though pulling straight from power system/alternator when it hits. the volts on the cap drop like they should but then it also dims the lights just as quickly. big 3 were not upgraded due to having no excuse on that one. wiring for the system is 2ga so well more than good enough. now just to figure out why the cap stays on. upgrading the alternator and moving it to the headlights or out of the truck entirely may be the next option. thanks for the help if there is any more.

Yeah - Haemo likes to stir - especially when it comes to caps....

As H said, more power out of the grid....
Problem with cars is that they have two "grids" - it is normally the alternator, but is the battery when the alternator falls short such as big audio surges, lamp & motor surges - and of course with big steady-state loads & when off. (The "normal" grid and "absolute zero" for my amp is the battery since it is only used in anger at camping spots with loud annoyances. A few minutes of directed Dystopia or DRI... otherwise a bit of BF's "Slip It In" LOL!)

Not that your system is that big.... but the dips suggest total load during "peaks" exceeds alternator output.

The other dc issue is the IR transmission drop. If the distribution cable is shared....

Yes - I am paraphrasing my last reply. Sorry.


I don't think anyone argues that caps don't work - that's demonstrable empirically - but a giga-Watt alternator and zero impedance battery in the engine bay will NOT prevent a dip at the boot mounted amp.   
My & others argument is that a (small & cheaper) battery is more effective than a cap - but that's a preventative & rip-off thing. If you already have it, may as well use it to remove or minimise surges & sags. (Until it blows & pulls down the system!)

Otherwise the cap problem is where people think it is some magical booster of power or power store.
They aren't. A cap is simply a FILTER - across a voltage source, it simply smooths out the ripple. It cuts the peaks & fill the dips - but only for a short time. (A battery does similar - it is often modeled as a big cap or infinite cap.)
The misunderstanding comes from the less educated coupled with selectively worded marketing.


I'd expect the cap to stay since they are connected across the amp supply which is normally connected. Very few switch the amp power externally (except if a 2nd battery and battery isolator are used, but then the 2nd battery powers the cap etc).

As to the amp staying on, I'll leave that for the amp gurus.

rscwboy wrote:

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A friend just bought a new truck; its a 2008 chevy silverado crew cab. Of course all new toys need more base and so weve installed a small system that sounds good; but somehow are still running into the general problem of his headlights dimming. The system is extremely basic and simple: 2ea Kicker CVT 12s, Power Acoustik BAMF 1800/2, 5 farad PA CAP in an aftermarket box fitted for the truck. I have done basic car audio before and am an electrican by trade, so figured it would be easy but am now baffeled and need assitance. Speakers are 400w RMS & 800w peak, so the amp is more than enough for them. Wiring was kept seperate, 1 speaker per channel, and the cap is mounted right in front of amp so wires are as short as possible. The base control knob that came with the amp doesnt seem to work so we just took it out of the system. And the third problem is the that the amp stays on constantly. After we shut the truck off, it will recharge back to around 14v but it stays lit up and we assume that its drainging off the battery. Any help with these problems would be greatly appreciated.

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You didn't mention if you changed out the head-unit or not. If not, then where did you tag your remote wire? The best place I usually go for an accessory tag is the ignition under the steering column. Make sure you fuse it.

And as many people have already said, a capacitor is not the answer to dimming headlights. The only way to fix dimming headlights is to upgrade the charging system. A new battery will help quite a bit, but the biggest help is going to come from upgrading your Big 3. You can do a search for "Big 3 upgrade" on here. Not only does it help your system, it helps the electrical in the rest of the car.

Good luck.

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MECP Basic Installation Tech
Certification ID: CEA195600
Pioneer AVIC-X920BT
Polk Audio DXi 6500 - front
Rockford Fosgate Power T1693 - rear
Alpine MRP-F300
Alpine MRP-M500
Alpine SWR-1242D

Yet again - unless the dip is in the transmission/distribution.

Over & Out!