I have a 91 Z28 that I've pretty much been through all the wiring due to the previous owners hacking. I put a new alternator on it when I replaced the engine and for several months all was well. Now at random times it jumps to 18 volts, the lights get super bright.

I thought it may be the regulator so I took the alternator and had it check and it checked ok. It's a lifetime warranty so I went ahead and got another just to be sure but it's still doing the same thing. Any suggestions other than the obvious?

I checked it with a meter just to make sure it wasn't a faulty gauge. Checked the wiring running to it. Checked all my grounds etc. I'm at a loss.

Donny

 

check or replace the bigger charging post wire from the battery pos post to the charge stud on the alt

if its damaged or high resistance it will cause too much voltage output

not good...

clean all connections and cab le ends real good clean and dry and tight

every single one counts

make sure, for sure, double check all

 

I think I finally found it. After I read your post, I pulled the wire all the way to the battery and laid it across the top of the motor. Slightly below the battery where the junction is at, the wire is joined into the bigger wire inside a molded plastic piece. while the car was running i can wiggle the wire and the volts go up. I bought a junction block and cut all that out and placed all in the block (I needed extra power taps anyway) and all seems well for now.

Thanks for the reply

Donny