View Full Version : Help with lights dimming after audio install

02-27-2008, 12:56 PM
I just finished installing the following into my 01 325i (non-xenon)

one 12" Infinity Sub 4ohm, 300w RMS (in vented box)
one Sony Xplod Amp 340w RMS at 4ohm (adjusted gain lower to match sub)
one Audiobahn 1 Farad Capacitor w/digital readout
one JVC MP3 deck with amp pre-outs

After the installation and tuning the bass I noticed that when the bass kicks hard my headlights dim. (even when the cars on and driving). I looked at the capacitor and it is kicking in and maintaining 11.5-12volts. I thought the purpose of the capacitor was to eliminate the extra drain on the battery.

Could the issue be that because the amp is 2 feet from the battery in the trunk and that the main power wire for the vehicle is longer than that, due to it having to travel to the front of the car to feed the fuse panel and other accessories it is taking too much power?

Any help would be greatly appreciated. Thanks

02-28-2008, 10:21 AM
Weird......... that's not a big amp either. Strange that this should be happening. Most stock electrical systems can easily handle this. IS there anything else aftermarket installed and running at the same time? When is this happening............. -20 degree weather when you have all your accessories on ???

02-28-2008, 11:09 AM
The car has nothing else electrical added. Only mods so far were suspension and wheels.

The car is kept in a heated garage but it does not matter if the temperature is above or below 0 the lights still dim when the bass hits. I have tried it with nothing else on except the radio and the headlamps while driving, and same results.

The Battery is only a year old and no other electrical stuff have been acting up. The car starts up first time and everything else works fine, heater, rear defroster, wipers, etc.

Just a thought but does it matter that I grounded the Amp directly to the battery negative terminal rather than a clean chassis screw/point?

Unfortunatley if this contiues I will have to remove the 12" sub and try a lesser system maybe with 2x 6" or 8" subs with a combined total of 200w RMS.

Any one else have the same symptoms?

02-28-2008, 11:23 AM
did you pre-charge the capacitor before installing? common mistake where the capacitor doesnt do anything after installation. To test it use a volt meter and see if there is a large drop.

02-28-2008, 11:41 AM
get a secondary battery :D

02-28-2008, 11:43 AM
sounds like the alternator is dying

02-28-2008, 12:14 PM
In reply to Blades question, yes I made sure the capacitor was fully discharged first and than charged it with the supplied light meter. I have done this many times with no issues.

In reply to jstalin comment, I will check my alternators output tonight when I get home with a volt meter. However I would have thought if the alternator was dying that when I have the heat on, wipers, rear defroster that the lights would dim but they do not.....I guess I'm F__Ked if it isn't the alternator either.

03-03-2008, 12:52 AM
it is your battery. The same thing happened to my brother 01 330ci. He installed a full system like yours and his lights were dimming. so he installed an optima yellow battery and it was great afterwards. hope this helps

03-03-2008, 01:01 AM
yea happened to me and i installed an optima blue top battery..... for rv's and boats's....:D

03-15-2008, 05:22 PM
you shouldnt ground to your battery

03-18-2008, 05:35 PM
you shouldnt ground to your battery

just wondering why?