Alternator Field Fuse Blows

[nik]

1999 Navigator...

Any one know what would cause fuse labeled "alternator field" to blow?

Had a problem where most of the electrical components quit working and then eventually the car died on the road. Wouldn't start.

Found this fuse blown, replaced it and had to jump start. Everything appeared fine afterward until the next day... same thing. Fuse blown, jump start.

Took to dealer who said run 'til it happens again since electrical issues are hard to trace.

[Steve Moran]

Hi nik.
Welcome to the forum.
How many miles on your vehicle? Do you have a aftermarket Amp?
Pull the alternator off and have it tested at an auto parts store, I think it is lived a useful life and will need replaced. Alternators these days work harder then ever, with extended hot run times it wouldn't be feesable to put in brushes and whatnot. The Diodes and armature have taken a beating long enough. If and when you ned to replace it CHECK all your connections for tightness and signs of over heating. Use Dielectric grease on your connections and you should be set for a long time to come

[nik]

Car has 90,000 miles with no aftermarket amp.

It seems rather funny to be the alternator because after replacing the fuse and jump starting... everything runs just fine. I guess that's the mystery of electronics. I'm not sure what resets the condition but if the alternator was bad, wouldn't it show up constantly?

When it occured, I could hear a relay clicking and the light under the hood would go on and off with the clicking...

I talked with a dealer again last night and they couldn't tell me what all was on the fuse circuit... does anyone know what this curcuit is for?

Dealer recommended a diagnostic check... if the alternator is the problem, can it be detected given that everything seems to be functioning fine now? I hate to pay a dealer to snoop around and not be sure they can identify the problem... Right now I don't trust the car for my wife and kids to be driving it around.

[Steve Moran]

sorry I was out of state for the last day and a half.
The dealer is full of beans, they have books on that stuff they just won't give any information for free.
I would say find the relay for the underhood light, swap it with a another relay from under your hood that has the same part number. If the light problem goes away, or whatever you switch relays with starts to act up then you have the problem salved.

[pepsi2185]

I agree the dealer is BS'n you. I hate dealerships. The relay clicking i suspect just the truck being low on voltage unless it was in the hoodlight. I wonder if something else on the alternator field circuit is grounded or drawing too much current.

I believe the field fuse is used to energize a magnetic field around the stator instead of using just a fixed magnet.

Where is that alternator located, yank it out and take that bad boy up to autozone or murrays and have them test it. Screw the dealership. You might as well double check it before you replace.

[ September 22, 2004: Message edited by: pepsi2185 ]

[Nick]

Here is another idea. If you continue to have charging issues and you know it's confined to the charging system, take the truck to a parts store like Advance, AutoZone, or the like. They can test your charging system for you for free. When I had charging trouble with a rebuilt alternator, it was a bad diode that intermitentntly worked. It took a couple tries, but the parts store diagnosed it with their tester.