Disabling Voltage Regulator?

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Oct 7, 2005
Columbia, SC
Before you tell how I am like the four millionth person asking questions about wiring a new alternator, let me tell you I have been reading threads for 6 days, and can't seem to find exactly what I need.

Here is the scenario: New 12Si alternator, new pulley, new mounting bracket. All is good there. Wiring the keyed 12 volt source with the original thick white wire that runs to the AM part of the ignition switch. 4 gauge wire from battery to battery lug on alternator.

The question is in the regulator. Mine does not have a harness like some pictured on here. So I was wondering the proper way to disarm it. I have a white with black going from the regulator towards the alt.. A white with green going towards the alt.. A white with red going through the firewall, and white with green going through the firewall.

So do I just connect some of these wires and remove the regulator, or do I need to run some of the wires back to another source? I believe the white with red goes to the flasher unit, and the white with black is a ground. What do I do with the white with green and should the white with red go to a 12 volt source?

Thanks for any help

You don't need a regulator for the 12Si, because it is internally regulated. You can just tape off the original wires or if it bothers you, remove the VR and tape off the wires going through the fire wall. If you look at the schematic diagram for the 71 that is in tech links, you will notice which wires to the VR do what. None of them are needed with the 12Si.

I don't really understand your description of how you have wired your 12Si, but if it works, it is all good. It is good practice to have a fusible link in the power output wire of the alternator to the battery so that you don't have a fire or melt down if the diodes in the alternator fail.
I haven't wired it yet. What I was going to use as my switched 12 volt source is the WL wire that runs to the engine bay from the - side of the amp meter. I haven't checked, but this should not be hot since the switch bridges the connection from the hot wire on the + side of the amp meter. Am I right in using this as my exciting wire?

The other wires I will just tape off at the regulator.

Also what size wire should I run to charge the battery? I thought I read 4 gauge welding wire. If so that would mean a pretty large fusible link. Am missing something?

Sorry to be such an idiot, but wiring really trips me up.

No, you don't want to use the old alternator B+ wire (white/blue stripe) that connects to the alternator because 1) it is not switched and 2) if something goes wrong and it shorts out, you will knock out all power to the chassis. Just remove this wire at the amp meter. There are a lot of options to excite the 12 Si. I think that the best is to simply use the existing "F" field wire (white with green stripe) that runs from the F terminal of the old alternator to the VR on the firewall. If you remove this wire at the VR and connect it to the white/red wire at the VR it will be hot when the key is on. Then you connect the other end of this wire to the ignition excitor terminal of the 12Si.

4Ga is overkill considering that the output of the 12Si is ~100A and you won't be putting out 100A continuously. A fusible link of 125A would be about right. You could also just get one off of a 12Si equiped GM vehicle at the junk yard.
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Thanks so much, your small paragraph cleared up days of reading. I will do exactly that and run with 8 ga. wire through a 12 ga. fusible link.


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