Alternator fuse keeps blowing

[notaprob]

1994 Ford Ranger 4.0. I'm having trouble with the alternator fuse blowing. It's the number 16, 15amp fuse in the power distribution box under the hood. I had the battery tested, and the alternator bench tested. Both are good. I had to have the alternator bench tested because it would not read on the handheld. I tested it for a short by connecting an ohm meter to the yellow/ white wire from the pig tail of the alternator to the ground and could not get it to ground. It ohm's out from the pig tail to the fuse box, so it has connection. The alternator begins to charge normally when I replace ther fuse but blows when I drive it for a few minutes. I'm thinking about running a jumper wire to see if it solves the problem. Have any other ideas?

 

[franklin2]

I would unplug the alternator harness and carefully inspect it all the way to the fuse box. It may have rubbed through somewhere that you can't see.

 

[notaprob]

Just to confirm, the wire goes straight from the fuse, through a connector, and then to the alternator?

 

[notaprob]

I also noticed on the drive to work this morning, when it gets to 3000rpm the voltage gauge would drop and battery light would turn on. As soon as the rpm drop below 3000rpm the battery light would turn off and the gage will return to normal. I ended up revving it to 4000rpm and then the fuse blew again. I will dive into taking apart the harness to see if I can find a short. Will a short in the charging cable from the alternator cause the fuse to blow also?

 

[franklin2]

I believe that is what the fuse is for. The fuse is not for the larger output wire of the alternator that actually charges the battery, its a smaller fuse for the controls of the alternator.

 

[franklin2]

This diagram shows the 15 amp fuse protects the yellow/white wire.