Bought the rig and he had cut the pigtail for the alternator off. Then, he ran the field wire into the dash to a cut-off switch, and then back out to the F terminal on the alternator via a spade connector. He explained to me that the diodes were bad so the switch needed to be on only when the engine was running otherwise the battery would drain current into the alternator.

Well, if the diodes are bad, then aren't you putting AC current into a DC system?

So I pull it out and take it into Schucks for testing. I noted that there was nothing at all hooked up to the S terminal. The alternator tested good so I looked up a wiring diagram for an '86 F-series. Has the stator wire going to the S terminal on the voltage regulator. Makes sense to me. So I start tracing the S wire from the v regulator and find that it doesn't go into the same harness as the rest of the alternator wires, it loops around (green wire) and runs through two other harnesses. I have yet to figure out exactly where it ends.

Am I missing something here? Are the charging diagrams different for diesels? Where is the stator wire?

Thanks
-Matt

 

It may depend on how bad the diodes are on what kind of electric you are putting out. Maybe only one or 2 are bad? enough to drain the batteries, but not so bad that it wont charge.

 

Well the alternator tested good twice in a row. I'm thinking that the diodes are just fine and whatever charging abnormalities are present are there because it isn't wired correctly.

 

This is for 87 but i think it's same for your 86. Check grid C-2-4 below for the wire colors to chase out yours.

 

According to that, the stator wire goes to the instrument cluster and because i have AC the stator wire never goes to the alternator. Interesting.

Thanks!
-Matt

 

The diesels were wired differently, and I don't have a diagram for a older diesel. But if you want to wire it this way, it will work. Just make sure your "s" wire coming from the dash does have power when you turn the key. If you verify this and it does, then you can wire like the diagram below and it should work fine. In the method below, there will be no connection to the "s" terminal on the alternator, obviously we don't have chokes.