Ford F-150 electrical problem

Our 1999 F-150 is having some problems. It just loses all electricity and dies as it's being driven. We have replaced the alternator (twice, first time we thought it was because the new alternator was defective) but it still does the same thing. My dad's mechanics can't figure out what's wrong with it (not the brightest mechanics) Anyone know what could be the problem? What should we check before we spend a bunch for the dealer to look at it?

Loses everything or quits because the battery went dead? Losing everything, I assume all goes dead, no lights etc? If that is the case, you need to look at the main fuseable links. This will be all power sources leaving the battery to the fuse block area. (not the large starter wire, but the smaller one) and many Fords used the fenderwell mounted solenoid, so the links would come from the battery side of the solenoid. IF you loose everything, you have an open close to the battery. If you have the standard fuseable links (smaller gauged wire inline on larger wire close to the power source) give it a tug. Tug is kinda hard. If its elastic, its bunred open. If it pulls apart easily, that may have been your problem. But its going to be in that general area.

The alternator is not charging the battery. So everything runs as long as the battery has juice, which isn't very long. sorry should have been more specific.

OK, Ford alternators were kinda weak. If yours uses the plug on wire harness for all wires (usually the large charge wire is bolted to a terminal, but some used only a plug type) then unplug it and look for a melted connector. There is 2 large spades, these are the output or charge terminals and if the connection becomes poor, it melts, and the heat from resitance melts it down, heat is also sent into the rectifier and damages a diode or more and results in low to no output. You will have 3 pins at the voltage regulator. Labeled as "A" "S" and "I", A means battery and is a sense wire. It senses battery voltage to determine charge rate, will have power all the time and should be the same as the battery. S terminal is stator and will have voltage when the alternator is charging. Usually used to turn out the light circuit. I is ignition, basically, this needs to have battery voltage with the key on, if it doesnt, it keeps the regulator off and it wont charge. Good point to start from. Now you will notice the 2 screw holes near the bottom, one has an arrow pointing to it reading "test", you can ground this while its running to bypass the voltage regulator to full feild it. IF you do this and it starts to charge, you know the regulator is bad. But caution on the full feilding. NMake sure the engine is just idling, if the engine is running fast, voltage can go way up and damage electronics. You will hear the alternator load down. It should make a nice even whistle or whine. If it sound noisy like a bad bearing when you full feild it, means you have a diode or more out in the rectifier and it runs out pf phase (alternators produce 3 phase AC rectified to a rippled DC and when a phase it knocked out, it gets noisy and it will also generator lots of heat in the stator) Easy to replace. Be careful not to ground the other side, you will get a spark show. Usually the other screw will be protected by a cover of some kind. Also, check the charge wire going to the battery. No corrosion, loose connections etc. New cars charge at a high rate and a poor connection will melt things down, unlike the days of old when alts charge at around 37 amps max. A picture of the regulator is below, you can see the ID terminals to pin check


If this picture doesnt look like your alternator, then lots wont apply, but basics still will. Oh, another note, an alternator with a working feild (rotor turned on by the regulator, required for charging) will become highly magnetized and the rear pocket bearing will hang on to a screwdriver real well. Touch the back bearing with a screwdriver and see. Residual magnetism will keep it lightly magnetized, look for a real strong magnet.

Good place to start TMDTech!

Also do the basics, check engine grounds, batt terminals.

Well thanks for the advice mdt tech, but my parents ended up taking in the truck (not to the dealer) to have it looked at anyways. I believe they did basically what you had said, but still did not find a problem. So they did further tests, still nothing. Ended up being a missing fuse. :bonk: Coincidentally, we started having this problem shortly after having a turn signal switch replaced by the dealer. Sucks.

Thanks again for taking the time to help me out. :excuseme:

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