[John F.]

Last fall I replace/ my altenator because I could only get about 11 volts out of my system, that didn't solve the problem but I found a bad wire connection on one of the coil wires. That fixed the problem until this spring now I have the same problem and I checked all the wires and they seem fine. Today I put voltmeter on altenator hot lead and got 11.75 volts coming out of it. I can't figure out what's going on, it worked fine a couple of weeks ago when I went to get gas but not anymore.
Help!

 

[rs7201]

Assuming you have an alternator with built in regulator. There is a screw on the regulator with an arrow point to it, marked "ground here to test". Have you done this?

Richard

 

[John F.]

No but I grounded it to the engine block, it's hard to get to the alternator on my truck

 

[1972Mach1]

If it's a one wire alternator you have to rev it up past a certain RPM before it gets "excited" and will start charging then. Have you revved it up and checked output then?

 

[John F.]

If it's a one wire alternator you have to rev it up past a certain RPM before it gets "excited" and will start charging then. Have you revved it up and checked output then?

Is 4000 RPM enough?

 

[1972Mach1]

Is 4000 RPM enough?

Oh, it should definitely be charging by then. It's usually 2000-2500 when they start working. Sounds like you got a bad new alternator if it's only putting out 11.75 V at the charge lead, and you're SURE it's grounded well. It happens.

 

[John F.]

Is the small wire that goes from spade connector on alternator to inside under dash the exciter wire? Where does it go?I have a Ron Francis wiring system and the wire from alternator is marked Alt. field.

 

[1972Mach1]

I was ASSuming you'd be running a 1 wire alternator, but apparently not. There's a few different styles of alternators. Google is your friend: Alternator Wiring Diagram: A Complete Tutorial | EdrawMax