Is it the alternator or battery?!!

[fordgirl]

I am stumped. I was driving and the radio turned off, all the advisory lights on the dash lit up and the headlights dimmed, gauges went crazy, till the truck completely lost power. Jumped it and it made it 100 feet. Jumped it again with all electrical loads off and barely made it the mile home. I found what appears to be a short on the ground of the alternator and taped it up. Had both the alternator and battery tested...auto zone said the battery was good and just needed a charge, failed the alternator 3 times. They then failed a new alternator off their shelf 3 times. Precision auto couldn't get a ground on the alternator to test it. NAPA passed both alternator and charged battery. Fine...but them both back in. SAME PROBLEM TODAY. What powers everything in the cabin (lights, gauges, etc) because I thought a truck could run on a dead battery because the alternator is capable of powering everything (and especially th cabin lights)???

 

[smokey]

Check the fuseable link on the fender well. it looks like a regular wire but has a slight bump or wider section in it. it may have blown and not allowing the alternator to charge. Truck will run on a charged battery for a brief time till the charge drops and can't power the ignition.

 

[fordgirl]

Wiring and fuses look fine. Battery is sitting at 12V engine off, so it's not dead and it will start. Gotta be the alternator right?

 

[Beach66Bum]

The reading on your voltage meter should read 14.4 volts when the engine is running.

 

[Beach66Bum]

If it doesn't change from 12 volts, I would suspect a bad alternator.

 

[dustybumpers]

Check theFUSEABLE LINKon the fender well. it looks like a regular wire but has a slight bump or wider section in it. it may have blown and not allowing the alternator to charge. Truck will run on a charged battery for a brief time till the charge drops and can't power the ignition.

Fixed it for ya smokey

 

[dustybumpers]

What year is it?
87-91 are G-2
92-97 are G-3

G-3 alternators do NOT have a fan behind the pulley
There is no fuseable link on a G-3

 

[dustybumpers]

Hard to diagnose her problem without the year, 86-91 had the 2G that melted the harness.
If it's one of those, they make a patch harness for it.

 

[kiwi f150]

Check your ground connection between the battery , body and engine

 

[fordgirl]

Solved

Voltage regulator wire was broken.

Thanks guys!