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Old 08-22-2009, 01:11 PM
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1989 Ford 150 charging system irratic

I have a 1989 Ford F-150 6 cylinder with an alternator with and internal regulator and voltage meter. The voltage most times does not go over 10 volts, which is probably why the engine is hard to turn over when it is warm.

I have found that I can break the connection of a green wire with a connector and which runs from the alternator to the positive side of the battery circuit and then reconnect it, the battery will charge. The engine revolutions will respond (slower) to this action. Unfortunately , after I shut the engine off, I am back to low output. I have change alternators with the same result.

This truck has been "repaired" from time to time before I got it and there have been signs that those that performed repairs may have made changes. In any case, I don't know what I have.

I have downloaded a wiring diagram and I think that the wire that I disconnect appears to have a fuse and a label: "HOT IN RUN". I do not know what "Hot in Run" means and I don't find a fuse in the connector, just a connection pin and socket.

Electric theory is not my strong point. I am assuming that the green line provides power to energize something but I am only guessing.

Because there are two multi-conductor electrical plugs that plug into the alternator, I can't really analyze the circuit and I am not sure that a good connection is occurring. Is it possible to purchase replacement plugs if I suspect a worn connection?

What can you tell me??

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Old 10-05-2009, 10:40 PM
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Little question, biiig answer. Since there has been work done to the vehicle, there a re a few preliminaries that must be checked.

1) Make sure, by removing and cleaning, that you have a good ground from your alternator to the engine, and from the engine to the battery. Replace any corroded cables.
2) Make sure, by removing and cleaning and testing with voltmeter both resistance and voltage drop, that you have a good hot path back to the battery.
3) Make sure, see above, that all the pins of all connectors are straight, and make good tight contact, and there are no funky repairs to the wiring. Replace/repair wiring as needed. Only use solder on the connections, not solderless crimps. Crimps can be used if you then solder them and use shrink wrap.
4) Remove the regulator and make sure, see above, that all the contacts are clean and that they are there, not worn off.
5) Retest the system.
6) If the system does not charge properly, then replace the regulator. It is available in the aftermarket for about $40.00. I've gone through 3 on my 93 Ranger without replacing the alternator itself. It bolts on the back of the alternator with (maybe) torx screws (yay)
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