Re: Alternator Wiring Help - Saabnet.com Bulletin Board


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Re: Alternator Wiring Help
Posted by Justin VanAbrahams [Email] (more from Justin VanAbrahams) on Wed, 1 Nov 2017 10:42:08

In Reply to: Re: Alternator Wiring Help, Jawerdna [Profile/Gallery] , Fri, 27 Oct 2017 21:39:45
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Something is connected to the wrong place most likely. There are two small wires in that general area that are connected to the instrument cluster - the exciter wire for the battery light and the sensor wire for the oil pressure sensor.

The exciter wire gets 12v switched power from the ignition switch. With the engine stopped, the alternator provides ground and the warning light bulb lights. When the engine is running, and the alternator charging, that ground disappears so the light bulb goes off.

The sensor wire gets 12v switched power from the ignition switch. With the engine stopped, the sensor provides ground and the warning light bulb lights. When the engine is running, and there is oil pressure, that ground disappears so the light bulb goes off.

The battery warning light has a diode in the path (or it should, my '85 did not!) to block backfeeding 12v, but the oil pressure light does not. If the wires were switched you actually might not be able to tell the difference since both lights go on with the key, and off with the engine, but you could end up with the alternator backfeeding the electrical system through the oil pressure light.

What you need to do is unplug both wires - sensor and alternator - and with the key ON, ground each wire and see what light comes on. Then you'll know which is which. Plug them into the right place and you're done.

As others have noted, you don't have an "original" alternator in there. It's not a problem, but you need to be sure you're connecting the correct wire (the ACTUAL exciter wire) to the CORRECT terminal on the alternator. As I mentioned elsewhere, newer alternators have newer features which should go unused - if the exciter wire is plugged into the wrong terminal, you will get weird results. There should be labels for each terminal back there - *probably* be labeled like B and D, other letters. Assuming that's how it is, you need "D+" connected to the exciter wire. "B+" is the big lug to the battery. There may be other terminals like S and W; we don't use those. If you have other letters post them up - they're standardized and can be deciphered.

posted by 12.195.130...

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