I am looking for a simple, alternator wiring schematic for a chevy gm 3 wire alternator with built in regulator.

Ive had magic electrical troubles with a 1974 el camino for a year. I finally removed EVERY, wire and electrical device from the car, sat down with autocad and the haynes electrical schematic and designed my own electrical system from SCRATCH, and with a desire to not use any OEM components and especially to remove that silly floppy plastic circuit board that was behind the instrument panel. Not to mention the confusing fuse blocks on the drivers side firewall. my turn signal/brake light design uses 4 relays, purchased at a local electronics supply, and 2 thermal flashers purchased at autozone, and a handfull of lighted toggle switches.

All has worked well up until last week, where after almost a year of reliable service my alternator quits working -diodes not dioding, kaput. I go and buy a new one, and it lasts three days, and im out in the drive scratching my head, about to strangle myself with my multimeter leads. There are no shorts in any wire or circuit on the car.

I have the three wire gm alternator, the post on the back i have wired thru a fuse and to the battery positive cable. I believe this heavy red wire to be the "BATT" wire that charges the battery. I have it fused, and this fuse at 30 amps does blow occasionally, and it seems to be the wipers motor sometimes causes it. So, during this witch hunt, ive disconnected the wipers, and also disconnected the heater.

the small brown wire in the plastic plug,#1 position, its going to a switch that is wired to the battery, and when i am ready to start the car, i send 12 volts to the alternator, which i believe is to the "exciter" circuit. I leave this 12 volts switch "on" while driving, and switch it off at shutdown. this circuit in my haynes manual shows to be part of the e-guages, and i wonder if I should turn this switch off after the car is running? I do it this way because as i found out, if i send 12 volts to the coil and 12 volts to this brown wire with the keyswitch, the engine still runs when i turn off power to the coil (which tells me the alternator is working as a bonus :)). this alternator wire used to go to the ALT in the dash idiot light. anyway - thats why its on its dedicated switch.

next, Ive got this heavyish red wire coming out of the plastic jack beside the brown one, and it I have connected to the 12 volt positive circuit as well, and i believe it to be a "sensing" wire, that being i beleive it tells the alternator/regulator to giddyup or whoa!. I could just as well jumper it to the post at the back of the alternator, because they ultimately end up in the same place - which is the positive post on the battery. i ran this red wire into my buss fuse panel to emulate what was once the OEM configuration, and because thats what was in the haynes manual.

whatever happens....i am continually blowing diodes out of the alternators??????? The only non stock electrical feature on this car is an accell 50,000 volt super coil, i dont have any radios or even interior dash or cab lighting so i know my alternator is not being overloaded, by devices anyway.

Im in agony here, and maybe someone can show me the silver bullet.

In return, I offer the world the most simple and clean autocad drawing schematic of how to wire a 74 el camino, and not use any of the in the column turn signal cams and all the stock wiring harnesses. at present i have NO DASH in this car, and only a small teather with a 6" square box which is wired into a flat 10" x 12" micarta panel mounted on the passenger side firewall. at a later date I can finish my dash and simply migrate all my switches to it. This 6 inch box has all auto store type toggle switches for all functions. I cant share this diagram with anyone and not make an ass out of myself until i can rest assured that i have tha alternator circuit done right. I think I have, but a growing pile of alternator cores tells me different.

Thanks for any help.

Tim Mcatee
Abilene, Texas
xapache (at) operamail.com

Tim,Sorry I can't be of any help with the problem at hand...You lost me about 1/2 way thru(no big deal,I sometimes get lost on the way home)but just wanted to welcome you to the site and hopefully someone will jump in and help shortly!See Ya!!
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Daryle "It's what we learn after we think we know it all that really counts!"

I think your problem may be because you are connecting 12V straight on to the '1' terminal on the alternator. Normally the idiot light drops this down to a safe level to excite the windings. If you've replaced the lamp with just a switch, you're not going to get the right voltage drop across it and are probably burning it out.
I recently had to go through the whole charging system on my Falcon before I realised that a GM alternator had been fitted previously and the Ford external regulator and wiring had all been bypassed !
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Spud
Watford Rods UK

This link may help you:

http://www.rmahc.com/alternator.html

Also, I think you may need a higher rated fuse on your 'BAT' line. Nearer the max output from your alternator, on those cold, dark, wet nights when the headlights, wipers and heater are all on.
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Spud
Watford Rods UK

Tim,
Welcome to SRS
I sent a scanned image in an attached e-mail.

Hope this helps,
Rod
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Rod

http://community.webshots.com/user/rphazen

Just one question.......how come? There are hundreds of thousands of that wiring harness running around with no problems. (just replaced a complete one on a 70's buick to make it look prettty again)) I also like to use the relays for turn signals on the older stuff so as not to clutter up the old small steering column.(but find the guys drive down the road with them on unless i install that annoying buzzer) My next question is were are you getting the alt from? I have seen the cheap discount part stores ..along with the reliance stuff that Napa and carquest sells fail at a rate of 7 out of 10. Thats pretty bad odds. I wont use anthing but delco rebuilts now and not very many problems. Now with the switch you have for the excite wire,i have left them on with no problems in the race car but i learned to wire it to the ign switch. If yours runs on after you turn the key off you have it on the wrong post. It should be on the acc side(not ign side) so it is not hooked to the coil on shut off.(some older switches wont work)If you have your mind set on using a switch just use a push botton or mont switch to excite as it does not need power except for start up. Wanna get rid of some wires? Put a one wire alt on it...or buy the kit to change yours over.(i can get you the # if you need it) The down side is you must bring the rpms up a bit to get it to charge on start up..after that its charges fine. I will just add one other thing but i am sure with all the changing around of wiring you probaly thought of it.......grounds..grounds ....grounds.... One from the motor to the frame...one from the batt to the frame...one from the body to the frame. No short cuts they all have to be there. If you need the # for the 1 wire kit let me know its pretty cheap. The wire that comes from the alt should go direct to the batt.(10 gauge with a bigger fuse than 30 amps..alt is probly at least 60-100amps).after that you can pick up power off the starter or another wire off the alt/batt for power of the fuse block...Dont run the alt wire into the fuse box and run stuff that way. Sure way for problems. Hope that helps a little....The manual you are using.....aint always correct. Heck i have the huge chilton wiring manuals for imports and domestic and they are not allways right so.......good luck..
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Honest officer i aint speeding
I am qualifiying!!!!!!!!!

Welcome Tim from a fellow Texan!
I have had 2 GM alternators in different cars (3 wire) and found that the 2 plug terminals are part of the idiot lite system that also allow excitation to get the alternator rolling. I put the 12 volts from the output (battery) to the plus terminal of the plug and a 12 volt bulb with a 15 ohm resistor across the bulb from the plus terminal to the exciter terminal. The resistor is there in case the bulb were to burn out to keep the alternator working. I have several schematics of GM and Fords that have essentially the same circuit. I have never fused the battery lead from the alternator for a couple of reasons. one, the starting current peak for some motors that start with a load on them can be high. The terminals of the fuse can also corrode at the contact points and create heat and sometimes melting of the holder or even the wire. This motor could be the fan motor and if it's a high CFM type, the starting current can blow a 30 amp fuse. Two, any wire in the circuit can cause voltage drop if it has a heavy load across it.
I'm not sure about the diodes except that if battery voltage were allowed to flow back to the exciter circuit, it might be trying to turn the alternator and with the engine stopped and the belt is tight, the alternator diodes will start to heat up and will eventually open. Diodes have more of a problem of being able to go open than shorting but I have seen shorted diodes and they put an AC voltage back into the system. On Ham radio installations it usually shows up as a loud buzz when transmitting.
Are you using fuel injection? Since the car is a '74, I don't know if it's been changed or not. I'm assuming it's original. I've run 12 volts straight to the exciter plug but not sure now which pin it was, but as I said, a light bulb will drop the voltage and limit the current to the smaller pin. When the engine is off, does the body of the alternator get hot to the touch more than usual?
As was pointed out, the name of the game is you can't use too many grounds!! And a good suggestion is to buy a one wire alternator. It's internal regulator senses the voltage and either lowers it or raises it depending on demand. I'm using one now and have had no problems at all. I also run #10 wire from the alternator straight to the battery connection on the starter.
I once did a car from scratch just as you did and ended up using 2 Radio Shack 10 amp DPDT relays for the single bulb on each side of the back to allow both turn indication and stop lights.. worked great for several years and its still going well for the gentleman that bought it.
Hope something of this will be a help to you!..also, you can buy diode packs for some alternators that are higher rated for current and voltage peaks than the originals. They're not hard to replace but I would suggest tearing one down first if you've never done it before. Good luck!
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Fred P.

check out madelectrical.com,lots of good info on their tech pages,especially one wire versus three wire gm alternators.
hope this helps.
later