I just recently have baught a yellow 1985 iroc z28 with a 305 tpi engine with 77,000 original miles and i am the 2nd owner to it when i got it home everything worked great until i turned on the light's. When i did the voltage gauge and oil pressure dropped along with the RPM gauge if anybody knows anything about this or what i can do to fix it please let me know i have a receipt were the original owner boaght a new headlight switch so i wouldn't think it would be in that. I realy think that it is in the dash assembly but not sure if you know anything please tell me Thanks Rodney

 

Check, clean, and lube the ground(s) and 12V connections under the hood.

 

Did the eng slow down at the same time or sound like it wanted to stall.If so the oil pressure, voltage, RPMs would drop together as well.Could be the alternators not up to the task or maybe a short in the headlight wiring.