this is my first post on here but iv been looking on here for about a month now and cant find any answers heres my question iv got a 91 z28 my headlights work for about 10 to 15 min then they start blink on and off i thought i was the headlight switch so i went and got one from advance auto parts and it fixed it for about a week now its doing it again i have also cleaned up the grounds...

 

Im having the same problem in my nephews 89 RS. Ive had it happen in my 92 RS.... I replaced the headlight switch and dimmer switch and it fixed it. You might want to try replacing the dimmer switch under the dash attached to the steering column. In the 89 that Im helping out with.... replacing those didnt fix the problem. Were in the process of replacing all the grounds now. My nephew also had alternator problems. Voltage kept dropping. Turned out to be a bad alternator plug. After fixing it....the voltage still bounced when accessories were turned on....example....turn signals on... voltage bounced up and down with each flash. He has a battery with the side mount and top mount posts. We put a ground wire onto a battery post connector and bolted it to the existing ground wire mounted on the inside fender wall. Voltage problem fixed! BUT..... lastnight he said his headlights shut off for about 30 seconds again. Hope some of this helps you out. Id really replace the dimmer switch though.