Hi all, I recently picked up a 72 F100 and have been working on getting it roadworthy. The PO made a real mess of the wiring so I replaced everything with a universal harness from Speedway Motors. Decided to do a 3g alternator upgrade while I'm at it. Anyway, I picked one up from AutoZone (P/N DL7734-6-11) and wired it according to :

It was working properly, ~14.5V. But then the next time I started it up, it was not charging. I took it back to AutoZone, they tested it and confirmed it was not longer working, and gave me a new one. Now, before I throw the new one in I want to make sure my wiring isn't what fried the first one. I believe my issue is with the "l" terminal. It's hooked up directly to a 12V ignition wire (hot in run/start). A friend said he thinks this is what fried it and told me there has to be a dummy bulb or resistor (or both) as in the diagram here:

I see that this has been posted about many times, but I can't seem to find the answer I am looking for. As I understand it, the "l" terminal acts as ground for the dummy light when not running. When running, the "l" terminal outputs an equal 12V, so equal potential on both ends of the bulb, no current, no light. I'm confused as to if a bulb or resistor is required for this circuit, since other posts people just mention hooking it to a 12V feed.
Thanks for the help!

 

For what its worth, I have the supply to the "I" terminal at full voltage from a relay that is triggered by the ignition. I converted my gauges to a voltmeter so I am not using any of the old ammeter shunt wiring and never had an "idiot" light. I have had zero problems with full voltage to "I" and I think that the factory cars with 3G did not use any resistors. The Mustang diagram is specific to the gauges or lights in the early Mustang.

The one difference that I was concerned with is the yellow wire. Notice on the first diagram they have it connected directly to the main cable at the alternator. In the Mustang version notice that they have the yellow wire going back to the solenoid. If you pull the wiring out of donor car you will see that the factory also runs the yellow wire back to the solenoid. I think that there can be a slight potential difference that helps with regulation when wired per the Mustang diagram. I have also read that it doesn't make any difference but when in doubt wire it like the factory. Given the quality of rebuilt alternators these days your's may have simply died from a poor rebuild rather than wiring.

 

The I terminal can go to any switched ignition source, make sure its not a hot in Aux source. The yellow wire needs to go back to the solenoid to get the most reliable voltage sensing.

 

Try this article:
https://www.hotrod.com/articles/inst...r-older-fords/

 

Current limiting the 'I' wire with a resistor shouldn't do anything. It's just a sense wire to turn it on.