Alternator charging at 15+ volts

Nealuss · Jan 2, 2017

Lately my alternator began charging at 15+ volts. I replaced the alternator, checked all the wiring, checked every ground under the hood and everything seems fine but it still overcharges. Reading 15.2 without a load and 15.8 to 16 with a load but never goes any higher. It may be coincidence but it seems like it started right after I had the intake manifold off doing the plenum plate upgrade. Alternator, a/c, etc. had to come off so not sure if anything could have happened there. Anyone have any ideas? Really hoping it's not the pcm because I need the stock pcm to get me by until I am ready for the 5.9 swap!

dudeman2009 · Jan 2, 2017

The charging voltage is controlled by the PCM. It is likely not a coincidence that this happened right after removing it to access the intake. You should have not just a positive charging lead, but also a second two pin sense and excitation plug on the back of the alternator. Make sure this plug is in and secure. Then retest your charging voltage.

Nealuss · Jan 2, 2017

Mine does not have any electrical connectors. It has a harness with a battery positive wire, 2 ground wires, and a block with two eyelets that bolt to the portion of the regulator on the alternator. All of that is connected properly not to mention I replaced the alternator after all of this started. Unless there is something in the block that connects to the regulator that could cause this I have no idea.

dudeman2009 · Jan 3, 2017

I didn't see that you had a 94, It should be pretty close to the 95 model (thats the oldest service manual I have). There should be 4 connections total. Battery positive, a ground wire, and two additional wires either in a connector or as two ring connectors in your case. Of those two outlined in red, one runs to the PCM for charging voltage control, there is no real voltage regulation occurring in the alternator itself, it is controlled from the PCM.

You may have connected one of those wires, but you may have dropped the other one.

One wire should be 18 gauge and dark green in color, the other also 18 gauge and dark blue in color.

I'm not sure if there is a way to tell which is terminal one on the alternator, so after hooking up the fourth wire nothing happens, try switching those last two.

Alternator charging at 15+ volts

Nealuss

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dudeman2009

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Nealuss

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dudeman2009

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