I am converting my 51 pontiac over to 12 volt and I have a brand new GM alt. in my garage that I am going to use. The plug on the back has 3 wires, a 10 gauge red, and a 12 gauge black and a 12 gauge brown. I am not exactly sure which wire goes to the black and which wire goes to the brown. Any help would be appreciated. Also, is it ok to use the original fuse panel because it is in really good shape, the contacts are clean, and the wires are good. I will be changing all of the wiring under the hood and tying in to the old stuff near the firewall.
you need to figure out if the alternator is internallly or externally regulated. do you know what it came off of, I believe the internally regulated started around 1974
You'll have to go and get a diode harness from an alternator rebuilding shop that connects between your two side wires and the harness. This keeps the current flowing out of the alternator, and not back in. I scratched my head for over 8 months trying to figure out why my battery would be totally dead after sitting for only two days. Finally, one of the guy's here at work told me about the diode harness, and that was the end of my troubles. It burned the brushes out of one alternator before I put it on. You must have it!!
The brown is switched ignition feed. Most will self energize if you leave off the small red and black wires.
Carefull there, one wire is not switched on ignition but 12 vdc felt thru a bulb, when the switch is on current flows into the alternator and lights the idiot lite, but has the bulb in series and doesn't get much current as it can take otherwise. Once the engine is running the alternator puts out more voltage than the battery, and the bulb goes out. If for any reason the alternator ran away and started to rise in voltage the bulb would light again, but only for a little while. If you install the alternator and dont plan on an idiot lite, the alternator may not self excite and charge. If you put it in and start it with no charge, jump this terminal hot briefly, the circuit should kick in then. Under these cir***stances you will need to put in some sort of an exciter circuit, you could hide the bulb under the dash or hood if undesirable for your project.
If the alternator has a provision for a female spade connector where the plug is for the 2 wires and a but with a stud on the back you can hook your main wire to the back and run a jumper wire from the #2 (they are numbered on the alternator) to the main wire at the back of the alternator. This works good in all of the cars that my uncle builds. And has worked good for me and my buddies builds. Hope this helps.
I've tried it that way, and burned up an alternator by not putting in the diode. The way you did it is the way I presently have mine hooked up plus the diode harness, and there's no problems, but you have to have the diode in it when you wire it up like that. If you put a test light between either battery cable and the battery, with everything off, you'll find that it lights. Unplug the two wire connector on the back of the alternator, and it will go out. You need that diode harness in there.
Okay now i have a question. I have a GM alt that says its a one wire. There is a dust plug over the 1 and 2 plug terminal so its really a 3 wire alt. So if I hook up the number 2 terminal to the batt area on the alt i need a diode in between the number 2 terminal and the batt area on the alt?
Asher, With a one wire alt. Just hook up a battery wire to the post and your done, all the other stuff is done internally. Normal Norman
but what if I want the fun light lol then i can still use the other stuff right? Got another question i hope some one reads cuz I don't want to start a new topic. Where can i get some step down converters for 12 to 6 volt? I need some for my fans.
I found one at my local auto parts. Ya need a guy there that's not some 16 yr old ****on pusher, but a real car guy. Like your smaller "real" auto parts if you're lucky enough to have one. If not Speedway's got em
The only bad thing about one wire alternators is that they don't charge until about 1800-2000 rpm, but once they start, you can idle back down to 800-1000 and it'll still charge. But yeah, with a one wire all you need is the one wire directly to the battery, or through an amp gauge to the battery.
That jumper wire in the diagram is the one that has to have the diode in it, but that's exactly how you do it.
Try your 6v motors on 12v they will probably be ok. If not ie they get hot you'll need to insert a resistor to divide voltage. Now the fun part, how much resistance do your fan motors represent and how can you double it with external resistance and yet size the resistor for proper heat dissipation. I'll be watching.
i found one on ebay for the fans but they want $18 per reducer. I have like 3 or 4 fans i need to reduce.
this the way i have run my altenators for years. no diode, no light, just like this, you have to give your engine a little rev and it excites the alt. and thats it, you dont need anything else to make it work.
EXACTLY right. No diode, a little goose of the throttle to excite, and gone. The goose just happens in normal use, and need not really be a concern
Hmm, well the gentleman at the alternator shop told me that if you don't wire it up with both terminals and the main battery wire connected, you'll have a drain on the battery and burn up the alternator, which is exactly what happened. With the diode harness on, you run the wire closest to the battery terminal to the battery terminal, and the other wire goes to a key on power source. This is the correct way to wire a GM 3 wire alternator.
I have to fab up a new bracket for my alt., but there is one problem, I can't get the belt to slip under the crankshaft pulley. I looked in the book and it only tells me how to adjust it, but not remove it. Anyone know of a trick to get it out from under the pulley. I need to remove it because with new brackets, I need a longer belt. The new alt. hits the block the way it sits now. The motor is a pontiac 268 (staight 8)
With a piece of wood on a floor jack, you should be able to raise the motor slightly by the oil pan, gently stretching the rubber motor mounts enough to slip the belt out
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