Alternator/Electrical Question

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Jun 12, 2013
Middle TN
Hey guys,

Electrical is not my strong suit so was hoping you all could give me some pointers here...

Got my first 40 a few months ago and the battery was dead. Got a new battery and all was good until a week ago when it went dead on me. Long story short, the alternator was bad so I replaced with a new one and a new voltage regulator.
Well, my new alternator is not charging and I can't trace back the issue.

I put my battery charger on and it got the battery up to 12.6V. If I crank her up then it drops to 11.6 at the battery. I'm getting 11.9v at the B post with the truck running and if I take the hot wire off then it jumps to 14.5. As soon as I put the hot wire back on the alternator then it drops back down to 11.9. I spent all afternoon messing with it and can't figure out why it drops as soon as I wire it back up. Its a brand new OEM voltage regulator but it seems to be down regulating too much. Am I missing something simple here?

Also, my headlights quit working tonight but the fuse is still good. Not sure if it blew both bulbs but have not had a chance to check it out yet.

Start with checking and cleaning the fuse holder clamps and the fuse.
For testing "borough" another fuse from the fuse block (Hey, it's weekend, the shops are closed).

The Battery-Alternator-Voltage Regulator circuit is kind of "Who was first? The chicken or the egg?
The Alternator needs the correct voltage from the VR. The VR needs the correct voltage (via a fuse) from the Ignition key, which gets his voltage from the Battery/Alternator. If there is a resistance somewhere in the line the circuit won't properly work. 9 out 10 times it's a bad contact problem. Most of the time fuse related and sometimes a bad corroded connector.

More info on this stuff: -► voltage regulator (ext) how it works

Good luck,

Hi Trailrunner,

Problem solved?
BTW, that little pigtail is for a capacitor (aka condenser) to suppress the noise made by the VR when you listen to good old AM radio stations.
No need to hook it up unless your the owner of such a radio.


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