I need help, I have noticed when I drive the voltimeter reads fine but then when I come to a stop with the brakes pressed the voltimeter needle goes down to about 12 and the lights dim but when I let go of the brakes and press the gas it goes up back to normal, I just had the alternator change this pass summer so I dont think thats the problem, actually today the needle came so far low that the low battery light came on. Has anybody had any problems like this?
by the way I have a 99 blazer

 

Does it only do it when you're pressing the brakes?

Or does it do it when your idling in park?

Do you feel your brake pedal doing anything funky?

ABS usually makes the lights dim when it kicks in...

 

the vehicle brakes fine, it happens when I'm at a stand still at a stop light pressing on the brakes waiting to go.

 

I'd get the battery and alternator tested, just to be on the safe side...

Otherwise you've probably got a bad ground... Make sure your battery terminals have a good connection.