'90 Ford truck charging system

Troubleshooting ideas here... do these trucks have a fusible link somewhere or a charge fuse that I'm missing? The alternator tests "good" by the parts store, but the battery light is on and the volt gauge reads real low, but sometimes will jump up to what I would consider "normal" while driving (battery light doesn't go out).

obviously the alternator's not charging as I've got a little under 12v at the battery posts while running.... I've checked and cleaned all the terminals between the battery and the alt (alt output hooks to one side of starter solenoid post).

This just happened earlier today after I washed the truck (not the engine bay)... maybe coincidence, as I can't figure out what else it could be... would a short somewhere cause this kind of behavior? Are these externally or internally regulated (I can't find an external regulator unless I'm not looking hard enough?).

Internally regulated. It's on the back of the alt. Check the harness that plugs into it, they like to get hot and melt.

The wiring harness looks good, I pulled the insulation off of it and nothing's burnt. Plugs look good.

Looking at that diagram, it looks like there is a fusible link in there, and I'm picturing right where it's at... tonight I'll check that and see what I find.

Brushes

My 1990 F250 would eat alternators. Had to replace them about every 3 years. Got so that I'd take a spare one with me, just in case.

According to the parts houses, they made both internally and externally regulated alternators for 1990 F250s with the 460. Mine happened to be internal.

skrause said:

Brushes

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Right, but if you read the original post, you'd see that I had the alternator tested and the parts monkey says it's working properly. If you've got money laying around to throw at my vehicle, you could send it to me... I'll try the free troubleshooting first. :flipoff:

TreeClimber said:

My 1990 F250 would eat alternators. Had to replace them about every 3 years. Got so that I'd take a spare one with me, just in case.

According to the parts houses, they made both internally and externally regulated alternators for 1990 F250s with the 460. Mine happened to be internal.

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Mine's internally regulated too it looks like.

I was messing around with the rig earlier that day, pulling some old wiring out from a snow plow setup, and I'm thinking that I may have shorted something out and burned up the fusible link.

NotMatt said:

Right, but if you read the original post, you'd see that I had the alternator tested and the parts monkey says it's working properly. If you've got money laying around to throw at my vehicle, you could send it to me... I'll try the free troubleshooting first. :flipoff:

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Been there done that with Toy alternators, same basic principals. Open it up and look at them, that doesn't cost anything.

:fawkdancesmiley:


Testing by parts monkeys means nothing to me. Last time I tried that the guy tried to argue that the same analog needle could show both voltage and amperage at the same time. He didn't even have a clue what he was doing.

skrause said:

Testing by parts monkeys means nothing to me. Last time I tried that the guy tried to argue that the same analog needle could show both voltage and amperage at the same time. He didn't even have a clue what he was doing.

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Very true....

In a few I'm going to rip apart the fusible link and see what it looks like... and if that doesn't yield anything, then I'll pull the alternator back off and pull it apart tonight.