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After much testing, swapping out alternators, checking fuses, and digging into diagrams, etc, I've determined that, of the the three wires that connect to the alternator (not including the large B+ post wire), the RED wire is dead and has zero voltage with Key On Engine Off. The other two wires in that 3-wire alt connector, the white and the yellow, seem to be doing what they should be doing and show close to battery voltage, which is about 12.6v at the moment. (Sidenote: the truck runs and idles very well... until the battery runs way down, of course.)


Anybody ran across this before and/or have a suggestion to troubleshoot the red wire? This wire is supposed to carry 12V from the ignition switch to the alternator, far as I can tell, but it looks like it's probably shorted/cut/chewed-through or something. I'm thinking I've got to trace the route through the entire harness, somehow, or just run a new wire from the fuse panel at driver's feet out to the alt. But, you can tell me if I'm wrong! 😀


I've got a question out on YotaTech about all this too, but I know people here are pretty quick to respond, usually. Thanks as always.

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Posted (edited)

Ended up having to run a new wire from 10A Engine Fuse behind driver’s kickpanel; the red wire on the 3-wire Alt plug is supposed to have continuity back to the Engine Fuse (IG2 wire I think it’s called), and it did not. Using a fuse tap made this pretty simple. 

Truck is charging again at 14.5V and didn’t even have to replace Alt. 


Edited by Ctgriffi
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