Okay I had no great reason to replace the electro mechanical regulator other than to think it may be more reliable in the long run plus the new Autolite cover(purchased from a big Kentucky Mustang parts retailer). Before with the electro mechanical regulator the alternator light NEVER lighted except at start and all seemed fine. I bought the electronic regulator(silver print non AC) and installed yesterday for my 1969 Cougar 351W. Now the alternator light comes on sometimes for about three or four minutes and then goes out for a while then repeat. So I checked the voltage at battery while car is running(alternator light not on) and the voltage is 14.48 volts regardless of rpm. I just came home and the alternator light was still on when I pulled in so I checked with voltmeter and the voltage was 14.53 volts and after a few seconds the alternator light went out and voltage was 14.49 again. And this all happened in the daytime with no headlights on. When I turned car off after the last check the battery voltage dropped to 12.74 volts in two minutes and is steady. I have no battery drain when car not running so no shorts. I guess I have a bad regulator? Or is the electronic regulator more sensitive and picking up some other issue I might have that the electromechanical unit didn’t? I should reinstall electromechanical regulator and forget the new electronic types? Can anyone tell me what they think?
The pin that goes to the dash cluster connector for the alternator indicator lamp has a purple single-strand resistor wire along with a black regular wire that is there for mechanical strength when the pin is crimped. More often than not, I have to re-crimp that pin to get back the 15 ohm resistance that should be on that line. I’ve also found that the other end of the resistor wire (located at an OEM splice of the ACC line above the ignition switch) sometimes fails—if I tug on the purple resistor wire, the resistance comes back from high values to 15 ohms. This may explain your problem…
At least your voltages look OK. I put the Marti Auto Works replacement on my 70 XR7 (42A alternator with ammeter rather than light).
Marti Auto Works - VR-6 - VOLTAGE REGULATOR
I believe this is an electronic unit, and I haven’t had any problems with it.
Edit - make sure your new regulator is well grounded to chassis. Mentioning this because those holes in the apron easily get stripped.
Is the resistor wire in the under hood harness or dash harness? The under hood harness I just replaced a few months ago and connectors are all tight when pushed in. Yea the light never came on with the old under hood harness, nor the new harness until I changed the regulator. Someone else mentioned grounds, the screws are all tight screwed into the firewall. Engine is grounded at back of head to firewall. I was just wondering if others were having regulators anomalies.
Resistor wire is in the underdash harness.