Wiring a 3G Mustang Alternator to an EB

Original Write-up by Todd Zuercher
Revised by Clint Eddy
What you'll need from the Bronco:

Intact factory wiring harness

*Wiring diagram (not absolutely necessary) the only reason you would need this is if your wiring is a complete mess, and I would recommend getting things like that in order before doing this upgrade.

What you'll need from the Mustang:

*Alternator harness. This can be found at your local junkyard, or by going to NAPA and purchasing just the plug for $18. The plug is all you really need, and is clean and new.
* 1-16 ga. fusible link (NAPA)

* 1-14 ga. fusible link (NAPA)

* 1-18 ga. fusible link (NAPA)

* Electrical butt connectors (solder type, heat shrink type recommended)

In the Bronco harness, trace back 'upstream' from the stock alternator/regulator wiring to somewhere along the passenger's side fenderwell. Open the harness and locate the following wires:

1. Black/yellow stripe wire, -10-12 ga.

2. Black/red stripe (73-'77) or black wire ('66-'72), -10-12 ga.

3. Green/ red stripe wire 16 ga.

On the Mustang plug, locate the following wires:

1 white/ black wire 14-16 ga.

1 green/ red wire 14-16 ga.

1 yellow/ white stripe wire 12-14 ga.

Make sure you have enough of the correct gauge wiring, and connect the following:

1.IF YOU USE JUST THE MUSTANG PLUG-- Black/yellow stripe wire in the Bronco harness needs to mate with a 12 ga wire that you run from the post on the back of the Alternator. These two wires will then go to the + post on the starter solenoid using a 14 ga. fusible link. I would assume that you could run each of these individually to the + post with their own fusible links, but I ran it the above way to keep from having more connections on my solenoid.

1a. IF YOU USE A MUSTANG ALTERNATOR HARNESS-- Black/yellow stripe wire to one of the black/orange stripe wires in the Mustang alternator harness. Connect the other black/orange stripe wire in the Mustang harness to the positive (hot) post of the starter solenoid using a 14 ga. fusible link.

2. *******Black/red ('73-'77) or black ('66-'72) wire in Bronco harness to a 16 ga. fusible link. Attach fusible link to positive (hot) post of starter solenoid. ********This step was omitted in my wiring, as it did not apply. I had a black/ red with that came from the “sta” post on my alt and went to ground. Whether this was correct or not, I do not know, but that wire was not needed, as you would not want to run + to – on any connection.

3. Green/red stripe wire in the Bronco harness will be connected to the green/red stripe wire in the Mustang alternator harness.

4. Yellow/white stripe wire in Mustang harness to an 18 ga. fusible link. Attach fusible link to the positive + post of starter solenoid.

5. Remove external regulator and lots of old, now useless, cluttered wiring from the truck! I removed a yellow wire, an orange wire, and the regulator itself.

Hook up the battery and look for smoke!  Get out your voltmeter and check for 14-15 volts at the battery positive post. My battery was at 13 volts and shot to 14.6. The norm is 14.4 to 14.7 from what I have read.

The # 1a connection above could be done several different ways since both black/orange wires in the Mustang wiring harness carry the alternator output. Another way would be to not separate the two wires and run one black/orange wire to the black/yellow wire in the Bronco harness. However, this means that the battery is receiving its power after running all the way back through the ammeter wiring, fuse block, etc. Tying one of the output lines to the starter solenoids hot post gives a short feed line to the battery.
*Don't skimp on the electrical connectors. I used NAPA Sure-Seal connectors that provide a solid, soldered mechanical connection that's well protected with adhesive-lined shrink sleeves. The connections from the new 3G Alternator to the solenoid need to be stable waterproof connections. Black tape and twisting the wire is not going to last, and could have adverse effects on your wiring.

This setup results in a much cleaner wiring harness under the hood! I was amazed how much old wiring I was able to remove with this transplant.

Some people recommend using the Mustang fusible links to hook up the various wires. I found it much easier to run down to NAPA and get brand new links off their electrical rack.

There will always be variations in this setup if your wiring has been changed. Please don’t hesitate to post to the EBML if you have any questions.

Clint Eddy


Page by Clint Eddy - last modified 08/25/01
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