Got home from work yesterday and something smelled hot under the hood on my '95 T-100 (3.4LV6). Popped the hood and the alternator was hotter than a firecracker and smelled like burnt wiring.

Popped it off and took it down to the local parts store and as expected it failed the test and the bearing started even whining during the test... so my guess was that the bearings had gone bad and eventually it wore thru the armature and shorted it out... so they ordered me a new after-market alternator...

Installed the new alternator today. Started up the truck and their was still a mild humming sound coming from the alternator. I let the engine run at idle about 2-minutes then shut it off. There was no check engine light during this whole time. But when I touched the alternator it was hotter than a firecracker again. I had to put on mechanics gloves just to unbolt it from the truck again. I didn't have the belt stretched very tight, so it shouldn't have pulled the armature over.

I took the alternator back to the autopart store for a retest, and it tested fine (it took me about 10 minutes to get it off the truck and down to the store and it was still fairly warm when they did the test). Since their test machine doesn't run at very high rpm, we didn't hear any whining sound from the alternator during the test.

Any thoughts on what may be going on here? Were the bearings faulty in the replacement alternator? or do I have some sort of short somewhere in the engine that is drawing heavy amps on the alternator when the truck is running? The battery seems good as it holds a good charge and easily turns the motor over. :confused:

Any troubleshooting help appreciated as I'm at a loss (and so were the techs at the autoparts store) !! ...I need Mustang to the rescue!!

Thxs.

Check the wiring from the alternator to the battery. If that wire has increased resistance, it will burn up the alternator as it will put a bigger load on the alternator. Heck...it might be a good time to upgrade that wire to a bigger gauge... ;)

How to upgrade the big 3 (http://www.the12volt.com/installbay/forum_posts.asp~TID~73496~PN~1)... ;)

Also...check ALL yer grounds...especially the one fer the block and chassis/body. Corrosion at the ground points will also create a bigger resistance on the charging system. ;)

Also...you might want to have that battery checked out anyways... ;)

Since their test machine doesn't run at very high rpm, we didn't hear any whining sound from the alternator during the test.

I had a 1997 T-100 DX and sadly, had to trade her in for my current ride. Those trucks are bulletproof.

I did not have any problems with her but I suspect (as mentioned above):
1) Wiring 2) Improper ground 3) battery.

Good luck and advise us what you discover.

Check the wiring from the alternator to the battery. If that wire has increased resistance, it will burn up the alternator as it will put a bigger load on the alternator. Heck...it might be a good time to upgrade that wire to a bigger gauge... ;)

How to upgrade the big 3 (http://www.the12volt.com/installbay/forum_posts.asp~TID~73496~PN~1)... ;)

Also...check ALL yer grounds...especially the one fer the block and chassis/body. Corrosion at the ground points will also create a bigger resistance on the charging system. ;)
Excellent Idea. Kinda what I was thinking, the old alt getting that hot may have deteriorated (when the wire ends get hot they fatigue and do not conduct electricity as well) some of the wiring causing excessive resistance like you said.