Pontiac Owners Club UK

Hi all

I was hoping someone here Might be able to nudge me in the right direction.
The issue I am having is my amp works perfectly up until I run the engine. It cuts out completely but decides to cut in when I use the brake pedal. Particularly when the rear window heater Is on.
It seems like the more electrical item I use the more likely the amp is to work. Weird huh??

I've changed head unit. I have tried running cables separately down either side of the Car and I have tried several different earth points. My wiring is good going straight to the battery and to the remote on the head unit.

I am wondering if It's due to having a small battery?
I have a firebird 3.1 v6 auto with an Ln075 battery. Is this battery causing these problems?

Hope someone c as help.

Mark

can you draw a quick diagram of how it is wired up? and post it up here?

There has got be some sort of wiring issue here, I wouldnt have thought the battery size will be the problem - if the battery was to small and low powered it would just go flat easily not cut the amp in and out depending what pedals your pressing - especially the fact that when the engine is running the battery will be receiving charge from the alternator and so i theory the amp would have more "juice" available to it!

I have known an amp to have a similar fault before, and it was the amp itself which was faulty.

Hmm the guy in uh hem.. halfords is convinced the amp is fine because it works with the ignition on.

Wiring wise its dead simple

[bat] -----[fuse]------ |Amp +|
[rem on stereo] ------|Amp rem|
[Earth on rear sanded inner wing] -------|Amp -|
Speakers are correct

Like I said if I push the brake pedal it cuts in. If I put the lights, fog lights and heated rear on then the amp starts to cut in more often. Feels like it builds up an electricity charge, only way I can describe it.
Hmmm so confused now.

is the power/neg. supply direct from battery or from under dash feed?

firemonk wrote:Hmm the guy in uh hem.. halfords is convinced the amp is fine because it works with the ignition on.

Wiring wise its dead simple

[bat] -----[fuse]------ |Amp +|
[rem on stereo] ------|Amp rem|
[Earth on rear sanded inner wing] -------|Amp -|
Speakers are correct

Like I said if I push the brake pedal it cuts in. If I put the lights, fog lights and heated rear on then the amp starts to cut in more often. Feels like it builds up an electricity charge, only way I can describe it.
Hmmm so confused now.

Dont listen to guys from halfords! worst thing you can do. They know nothing of the nature of electrical faults. Just because the amp appears to work fine with just the ignition on does not mean it hasnt got an internal fault.

However, what i would do is run a new earth cable from the amp earth terminal directly to the battery negative terminal. See what happens then. It sounds like an earthing fault to me. Dont do it permanently to begin with just bang a cable out the boot and over the ground to the battery first to test it. Without being there with a multimeter its difficult to say whats wrong.

Thanks. I will try that. Might also find someone local who has an amp they wouldnt mind swapping over to see if it has the same results.

So there is definitely no kind of funny wiring on a 3rd gen bird that restricts electrical flow when the engine is running?

no, only thing is alternator has a built in voltage regulator (like all alternator equipped cars)
have you tested voltage while running?

The only other thing I can think of is that the alternator is generating a too high voltage which is causing the amp to turn off. Then when the brake lights or Demister are on they create a large enough voltage drop to allow the amp to work ok.

No I havent had a chance to play with a multi meter. Not even sure how to

So that would be a fault with the alternator the could possibly cause this? I have actually just replaced the alternator and havent tried the amp with this new alternator on. Thats a job for this evening then. Will keep you posted.
Thanks again for all your help

bhm1712 wrote:The only other thing I can think of is that the alternator is generating a too high voltage which is causing the amp to turn off. Then when the brake lights or Demister are on they create a large enough voltage drop to allow the amp to work ok.

Forgot to say here that large volt drops are also characteristic of bad earthing. To diagnose this is relatively simple due to the symptoms - put all your headlights on and put the hazards on. If you see the dash volt meter fluctuating in time with the hazard flashing then the earthing system is not 100%. My 2nd gen suffers from it mildly but doesn't cause me any issues and you will find that a large percentage of classic cars have it. Over the years the chassis metal becomes more resistive due to corrosion, and normal deterioration of the metals properties as well as the deterioration of wiring etc. it may look clean and new on the outside but the copper or aluminium conductors on the inside are not.

sounds like a earthing issue to me but need to check alternator voltage first should be 13.5-14.8volts engine running
a large amp will need a direct positive (fused) and direct negative from the battery they suck large amounts of power and is very bad to run any other way you could cause a fire if your trying to run any other way! you need very large guage cable to run them normally

Could be shorting at the head unit. Disconnect the remote wire from the head unit then run one direct from the battery to test it or for more permanent wire a switch inline. My amp cuts out but i have high power sub and the amp will overheat if ive had it turned up to 11 for to long!
That said, my bet is on the inline fuse in the amp main positive cable. Ive had many times where amp cuts out randomly and its turned out to be that 60amp fuse. I assume ur running a 40amp fuse in urs? For 3 quid its worth a try.