smh00n 87 Report post Posted July 28, 2019 I changed the alternator on my 70 to a 100 amp unit. The PO had already done this and didn't use the original voltage regulator but had an idiot light installed. I didn't really check how it was done, but they had cut into the 2 wires coming from the harness, ran a wire to the light and back and then into the harness. The other wire came direct from the alternator into this harness. I've tried a few different things; a wire direct from the output terminal on the alternator to a switched wire at the ignition switch has the light on when the engine is running and off when not. If I try to plug the 2 wires from the harness, it powers the MSD box and causes the engine to diesel on shut off. 1 wire is hot all the time and 1 is switched with the ignition. I've looked at all the wiring diagrams and I can't figure out what to do. Any clues? Surely I can just run a wire to a new light on the dash and it will work?? Quote Share this post Link to post Share on other sites
Mach1 Driver 560 Report post Posted July 28, 2019 Is yours a 3G alternator? If it is made by PA Performance it will have a special external regulator. If it is a Ford style 3G it will not. Below is a 67 with a Ford type 3G. I've looked at 66-70 and they are all electrically the same but the wire numbers, color and exactly where the wires connect may be slightly different, but the electrons still flow to the same places. Power for the added goodies should come off the starter solenoid post. The mega fuse will disconnect the alternator from the car, while the fuse link disconnects the car from the battery/alternator. Both are needed. The resistor in parallel with the light will let things work if the light burns out, and the light is not required. Its hard to tell, but it connects to "I". Quote Share this post Link to post Share on other sites
smh00n 87 Report post Posted July 29, 2019 No It's a no-name brand from here in Australia. It is internally regulated and self-exciting. The light I have needs a ground so I'm not sure how to do it (I am rookie sparky), plus it is LED. I was told I needed a filament bulb but not sure if that is correct for a self exciting alternator. If I wire in the light from the "I" terminal to a switched 12v wire on the ignition switch it only lights up when the engine is running, not when it is not. Do I need the resistor and/or a filament bulb? Quote Share this post Link to post Share on other sites
Mach1 Driver 560 Report post Posted July 29, 2019 9 hours ago, smh00n said: No It's a no-name brand from here in Australia. It is internally regulated and self-exciting. The light I have needs a ground so I'm not sure how to do it (I am rookie sparky), plus it is LED. I was told I needed a filament bulb but not sure if that is correct for a self exciting alternator. If I wire in the light from the "I" terminal to a switched 12v wire on the ignition switch it only lights up when the engine is running, not when it is not. Do I need the resistor and/or a filament bulb? It sounds like a Ford type alternator. If so you need at least a 1/2w, 470-560 ohm resistor connected to the ignition switch and active in "start and on" on one side and "I" on the other. If you want a light it should be a filament bulb - something like an 1895 or 194, both of which are 3.78w at 14v. Put it in parallel with the resistor. If its a Ford type internal regulator then that should do it. Quote Share this post Link to post Share on other sites
danno 128 Report post Posted July 29, 2019 It might help to see a picture of the alternator and the wire connections? How many wire connections does it have, and what are the labels on them? Quote Share this post Link to post Share on other sites
smh00n 87 Report post Posted August 2, 2019 Well I feel like a goose. Not checking properly and dirty terminal was the issue. Plus I was using an LED light which didn't have enough resistance. Used a bulb light, cleaned the terminal and all is working. D'Oh. Quote Share this post Link to post Share on other sites
