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NEWFISHER · 08-04-2014, 08:49 PM

I am in the middle of the Gen to Alt conversion and I am also using a 3 wire GM alternator. Here is a good write up that Ray did that I though I would cross contaminate the confusion

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First, you will need an alternator. It should be an SI type which was used on GM cars and trucks from the mid 70s to mid 80s. This type can be identified by having a plug-in connector with two flat blade terminals marked 1 and 2. If available, also get the matching plastic connector, which will probably have two short wires attached to it.

Next, get a small lamp socket suitable for an instrument panel bulb. The only requirement is that it must have two leads or terminals, and they must both be insulated from the socket mounting. This one from Radio Shack will work if you can't find anything else.
http://www.radioshack.com/product/in...ductId=2062366
Also get a 12-14V bulb that fits the lampholder, similar to this one.
http://www.radioshack.com/product/in...ductId=2102801

At this point, disconnect either one of the the battery cables and mount the alternator on the engine, but don't connect any wires to it yet.

The 3 terminals on the regulator should be marked BAT, ARM (or GEN), and FIELD (or FLD). Connect the BAT and ARM (or GEN) wires together with a small screw and nut, and tape up the connection so it can't short out against anything.

Get a length of 18 ga wire long enough to reach from the regulator to inside the cab near the ignition switch and connect one end to the FIELD wire. Tape that connection too. Connect the other end to one terminal of the lamp socket. Connect the other socket terminal to the IGN terminal of the ignition switch or to any other point where the power turns on and off with the switch. Mount the socket where it will be out of the way and the terminals won't short against anything

Now go to where the generator was, or where the alternator will be, and you should see two wires. These will be the other ends of the ARM (or GEN) and FIELD wires you saw at the regulator. Connect the ARM wire to the BAT stud on the alternator. Connect the FIELD wire to the #1 plug terminal and run a short jumper from the #2 terminal to the BAT stud. This completes the wiring.

Reconnect the battery cable. If you get a spark when the cable touches the battery post, disconnect it immediately and look for a wiring error or a wire shorted to ground.

If the wiring checks out ok, turn on the ignition switch, but don't start the engine. The bulb you installed should light, which indicates that the alternator is probably wired correctly. Now start the engine, and the light should go out, which means that the alternator is charging. You should also show a charge on the ammeter if it is wired correctly.

Ray

08-04-2014, 08:49 PM	#6
NEWFISHER Registered User Join Date: Sep 2012 Location: Oregon Posts: 3,303	Re: generator to alternator conversion I am in the middle of the Gen to Alt conversion and I am also using a 3 wire GM alternator. Here is a good write up that Ray did that I though I would cross contaminate the confusion . . First, you will need an alternator. It should be an SI type which was used on GM cars and trucks from the mid 70s to mid 80s. This type can be identified by having a plug-in connector with two flat blade terminals marked 1 and 2. If available, also get the matching plastic connector, which will probably have two short wires attached to it. Next, get a small lamp socket suitable for an instrument panel bulb. The only requirement is that it must have two leads or terminals, and they must both be insulated from the socket mounting. This one from Radio Shack will work if you can't find anything else. http://www.radioshack.com/product/in...ductId=2062366 Also get a 12-14V bulb that fits the lampholder, similar to this one. http://www.radioshack.com/product/in...ductId=2102801 At this point, disconnect either one of the the battery cables and mount the alternator on the engine, but don't connect any wires to it yet. The 3 terminals on the regulator should be marked BAT, ARM (or GEN), and FIELD (or FLD). Connect the BAT and ARM (or GEN) wires together with a small screw and nut, and tape up the connection so it can't short out against anything. Get a length of 18 ga wire long enough to reach from the regulator to inside the cab near the ignition switch and connect one end to the FIELD wire. Tape that connection too. Connect the other end to one terminal of the lamp socket. Connect the other socket terminal to the IGN terminal of the ignition switch or to any other point where the power turns on and off with the switch. Mount the socket where it will be out of the way and the terminals won't short against anything Now go to where the generator was, or where the alternator will be, and you should see two wires. These will be the other ends of the ARM (or GEN) and FIELD wires you saw at the regulator. Connect the ARM wire to the BAT stud on the alternator. Connect the FIELD wire to the #1 plug terminal and run a short jumper from the #2 terminal to the BAT stud. This completes the wiring. Reconnect the battery cable. If you get a spark when the cable touches the battery post, disconnect it immediately and look for a wiring error or a wire shorted to ground. If the wiring checks out ok, turn on the ignition switch, but don't start the engine. The bulb you installed should light, which indicates that the alternator is probably wired correctly. Now start the engine, and the light should go out, which means that the alternator is charging. You should also show a charge on the ammeter if it is wired correctly. Ray __________________ GOD BLESS AMERICA!