Odd electrical issues - '88 S4 Turbo II
 

When I'm driving at night, I pop my lights on. I noticed that when I'm at idle, the gauges are very very dim. When I start driving, all lights that are on brighten up. I even hear the fuel pump sound like it's getting extra power. When I get back to an idle, the pump gets quieter, my lights dim down... it's just weird. But the odd thing is, my gauges don't even get that bright when I'm driving, it's still very dim. All the lights on it are good and I know this because out of the blue, they completely lit up for a quick moment and dimmed back down. Anyone have an idea of what's going on? I'm thinking it is a ground issue, but I don't know where any of my grounds are. Thanks

It's probably because your alternator is not producing enough voltage output. You have a Black cable connected to the alternator that is the output wire. Voltage measured on this wire should be 14.4 volts at all times while the engine is running.

Could be that, I'll get that checked even though it's pretty new.

The alternators you get at the local parts stores are mostly useless.

Well I just got everything tested, they're dumb tester said everything is good. Although, the guy did mention that the tester doesn't pick up on little things inside the alternator. Still debating whether it's a bad ground or not. I also forgot to mention that my right blinker blinks fast as if one of my bulbs were bad but they're both good. It's also pretty dim too compared to the left blinker which doesn't blink fast and is brighter.

Sounds like more low voltage, like satch said. Do you have a voltmeter? The tests they run at those stores are useless too and the results are just as easily determined by the behavior of the car. Re-doing your grounds is never a bad idea though, but I'd also start looking for another alternator. Time for an upgrade.

I'm such an idiot.... -___- I never realized there was a dimmer on the side of the knob for the lights.

Clean up your room. Now!

At idle, the stock system will drop voltage to the pump for emissions and fuel economy reasons.

That explains a lot. Cause it is very obvious since the pump can very much be heard.