I have a feeling my voltage regulator (in the alternator) is going out. My voltage spikes to 18 right after I turn the car on. It has done this twice and both times were in the rain. Last time I turned all the accesories on and it went back to normal (13) after 10 minutes or so. This time the voltages only goes down to 17 when all of the accesories are on. UMMMM guages start flashing, abs inop!!!! Brakes!!!! Check Gauges!!! ahhhh Does anyone second that it is the alternator/regulator?

P.S. it is a 98 z28 M6, no after market radio or any other weird accesories

 

Sounds like a voltage regulator. Probably a good idea to get it fixed pretty damn soon.