Low voltage while running OK when not

[Kerplunk]

Hi there,
I'm having an electrical issue with my newly acquired 67 Belvedere II, it has a new chrome alternator and looks like a new voltage regulator.
A few days a go I noticed it was getting a bit hard to start, Like a the battery is weak. Now that has progressed to low voltage while the engine is running, the horn barely works, the lights are dim. But if I turn the car off, the horn works fine, and the lights are bright.

Im not sure its related but over the weekend I managed to short out the starter relay and got a nice spark when taking off the drivers side Valve cover. Lesson learned.

Electrical isn't my strong points so if someone could point me in the right direction Id be grateful.

Thanks!

 

[bluefury]

low voltage....

low voltage while the engine is running, the horn barely works, the lights are dim. But if I turn the car off, the horn works fine, and the lights are bright.


Could be a couple of different issues.

Is the belt tight...?

Try this.... with the engine running disconnect the battery + cable. If the engine stops you have a alt issue or to low setting on the regulator.

Be sure the engine is grounded to the body. OEM ground is a cable between the intake mainfold and firewall.

A defective diod or grounded stator windings in the alt will result in reduced voltage while running. (rebuild or replace alt).