Car = Supercharged 94 GSR

So heres the problem...



At night while I am driving I notice that the lights go a little dim. So I usually push in the clutch and rev it a little and they usualy brighten up again. every once in a while though they just go dimmer and dimmer.

Heres what I have done already...

I used a volt meter to measure the current while car was on, it reads out 13.68 amps, so thats all good.
I checked the alt. at auto zone, its good.
And I checked all the grounds on the car. They are all good

Any suggestions on what it could be? Reps given to any helpful advice at all as usual.