Posted by apb (in NY) on Sunday, July 02, 2006 at 2:51PM :
In Reply to: One wire alternator question posted by Bruce B.(ND) on Sunday, July 02, 2006 at 2:15PM :
First, I highly recommend that anyone who is going to trouble-shoot a vehicle should get an inexpensive digital multimeter ($20 or so at Radio Shack, etc) and learn how to use it.
So-called one-wire alternators can often have two or three wires. The big one is obviously the one that sends the high-amperage charging current to the battery. The other one or two are used for exciting the alternator and/or for the idiot lamp.
If you look at your alternator, you may see a small plug-in connector on the rear. The excitation wire and the idiot lamp wires are attached to a plug that plugs in at that location.
There needs to be a switch (generally the ignition switch) between the excitation wire from the alternator and the battery. If not, the battery will discharge via the alternator.
Do you have such a connector and wiring on your truck? If so, unplug the connector, and put an ammeter between the connector and the wire. If you get a reading, that's where the leakage is. That means the truck is wired incorrectly.
If there is only the one big wire, then you need to test that wire for leakage. With the engine OFF, detach the big wire, and put your ammeter between the big bolt terminal and the big wire. There should be neglible current draw. If you see a currect on the meter, then one or more of the diodes in the alternator is shorted. They can be replaced by the DIY'er.
When testing, remember that you can instantly cook an alternator if you disconnect it from its battery while the engine is running.
There are many articles on the web that can help you understand and correct your problem. Below is a link to a Google search for "one wire alternator"
Hope it helps. APB
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