72 C20 voltage regulator question
 

Hi all,

Hoping to get some help with a charging issue I'm having with my '72 C20. It uses an external voltage regulator (EVR). For some background, I recently completed an engine swap (old 402 out, new 540 in) during which I put brand new wiring harnesses in under hood. Alternator is also new. When I start the engine, the alternator does not kick in. When I disconnect the ground wire from the EVR to the radiator support, the alternator kicks in and starts feeding the battery. That's the opposite of what I'd expect given that the EVR needs a good ground. I found this out by accident while checking for voltage at various wires (tan at the EVR plug, white at the alternator plug) as I've seen suggested elsewhere on the forum. I've also tried a new EVR. I've consulted the wiring diagram but am not sufficiently knowledgeable on how charging systems work, so would appreciate if anyone here could help me troubleshoot. Thanks in advance!

Grant

Re: 72 C20 voltage regulator question
 

OK I figured out my issue - on the base of the EVR there is a terminal that sticks out the side - it used to have a capacitator attached to it, and the capacitator was attached to the firewall. I thought it was like that when I bought the truck - I guess I got the re-installation wrong. I assumed this was the ground. It's not. Grounding this out was causing my issue.

Re: 72 C20 voltage regulator question
 

Glad you got it figured out! I had zero ideas.....

Re: 72 C20 voltage regulator question
 

Welcome to my world of self Inflicted misery. Good job on figuring out the problem!