hey buddies, I have a 94 F250, I have had trouble getting the truck to charge the battery, I am on my fourth alternator, the alternator I have in and the last alternator which I still have have checked out to be good at the armature rebuilders store. the alternator has a built in voltage regulator, which the armature rebuilder thinks is good and I have replaced the plug ins. in addition I have checked all the wires for continuity, reworked my battery cables, cleaned up all the connections to the solinoid battery and grounding on engine block, frame and added an extra groung to the alternator housing. All the fuses on the fender in the engine compartment and on the dash check out good. I have a voltage gage on the dash and it shows to have a charge around 11.5 when I put new or recharged batteries in. The truck will start and run but appears to ber only running on battery power since the gage will slowly drop if you drive it in the day or run the power out fairly quickly if you drive at night with the lights on or with the heater on. I have tried to excite two of the alternators to charge using a jumper wire because the alternators are checking out as good. One of the wires coming out of the alternator voltage regulator is yellow with a red stripe and has power, the white wire coming out of the regulator and going back into the alternator does not seem to have power nor does the other green wire with red stripe that runs aroung the front back to the fire wall. My sisters has the same set up on her truck and is getting power out of all three wires. Do you have any ideas on what I might try next.

 

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I have this same problem myself. I purchased a 1991 F150 4x4 on Monday and have been through 2 alternators and three batteries by Saurday and have not figured it out yet. I replaced the plugs on the wiring harness to the alt. and ohmed out the wiring and all checks out good. The new batteries and alts. tested good till I put them on the truck and then the alt. will not charge. The battery is all that the engine is running off of and I have to put a charger on battery every day to run truck and eventually the battery reads bad and have to replace it. I do not see any fuseable link or other fuse associated with the alt. so do not think that is the problem. I have had a couple of guy's look at it and have put a volt meter on it myself and only read battery voltage with truck running. When you pull the battery cable engine will die instantly. Makes you think the alt. is no good but as I said they tested good before install. I know this does not help you but somebody might have a solution.

 

Holey crap guys:


I once had a chevy truck that had a short and was sending too much power to the battery..

sorry that's about all I can think of, a short somewhere

Good luck

 

The green with red stripe wire is supposed to be hot with the key on. That is what "turns on" the alternator. You are going to have to get that one right, or you will never get a charge. Could be broken wire, bad fuse, bad connection, problem in the instrument panel.
You could test the alternator, by temporarily running a wire to replace this one straight from the battery. Alternator should charge . DO NOT leave the temp wire connected, after testing. It will drain the battery pretty quickly, and not do the alternator any good either.
Good luck Frank

 

Are you getting a different regulator with each alternator, or the same one transplanted? If it's the same one then it's bad, period. The go/nogo bench testers are useless, they won't tell you if the internal regulator/rectifier is shorted.. and that is what's draining your battery.

 

Each new alt. had an internal reg. I talked to the used car dealership where I bought the truck and they told me to bring it in and they would look at it. I will tell them about the green wire as I did not have a voltage on it. This could be the problem and maby they can fix it. I have to take it to them anyway as the second day I drove it the main seal on the transmittion started leaking. Will let you know what they find on the alt.