Charging Problem

03-10-2008, 09:34 AM
I've got a 75 D200 with a 318. I put a good alternator on it cause the old one went out. My problem is that while the truck is running, it only registers 10-11 volts, and it doesnt charge the battery. I was starting to thing that it was just running off the battery because when I pull the cable off the positive side, it kills the truck, but when its running, it keeps a constant voltage, even though its low. Only other thing I can think of is the voltage regulator, but I'm not sure (not used to working with this external regulator setup. Any ideas?

03-12-2008, 05:50 PM
A fully charged battery should read about 12.5 or 12.6 volts, with nothing turned on, and the engine shut off. Anything lower is either a partially discharged battery, a battery with a bad cell, or a bad electrical connection. When the engine is running, the normal voltage at the battery terminals is going to be over 13.2, and more like 13.8 to 14.0 after it has been running for a while. Anything less is a problem needing to be found and fixed.
If your alternator is good, and the connections from the VR to the alternator are good - then replacing the VR would be my next guess. They arent too expensive, and they can quit working suddenly, with no warning. Sometimes the mopar VR's will act as if they arent working for a while, then will go back to charging the battery for a while, then do it again. This is a sign of being near-death though.
If you replace the VR and it still wont work, I would advise checking to esnure the alternator is grounded. I dont mean grounded to its own bracket, but by running a wire from the case of the alternator to the frame of the vehicle, or to the negative battery cable. This cable should be at least a #10 wire, if not a #8. I may need to carry 75 or more amps for brief periods after you start the engine.
Also; anytime the ignition is one, one of the two small wires in the connector going to the Alternator should have 12 volts on it. These two wires feed the field coils that are spinning around inside the alternator. The other wire is the one 'controlled' by the VR. The method of control is to ground the wire. This makes the alternator go to full output. The VR will then rapidly disconnect/connect that one wire to ground in order to obtain the needed output. Therefore it wont be easy to measure the voltage on that wire by using a digital Voltmeter.

As far as I know, the way the Volt. Regs. work is by connecting one fot the field wires to ground. The other field wire should always have 12 volts on it. So if you measure the voltage on the two field wires (the small wires going into one connector on the Alternator), you should be able to short the other one to ground, and have the alternator putting out its maximum. Be sure the alt. and the battery are connected up, or the full voltage from an alternator can

03-14-2008, 03:14 PM
I managed to find the problem. The voltage regulator itself wasn't grounded good.

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