Voltage Problem...

[slowrolla97]

Ok this problem is starting to piss me off. Every time I hit the brakes my cars voltage drops to about 13.0 and the cars idle will drop to about 500 and some time it will cut off. I have no idea what could be causeing this. I thought it might have something to do with vacuum but there are no vacuum leaks or anything. Do you think there is a problem in the brake light circuit? If you have any input please chime in. I am stumped on this one.

Edit: This is in a black top sr20 s13 hatch.