Two wire GM alternator to ignition switch?

Have a GM alternator on my 8BA in my '36, wiring instructions say to run yellow wire from connector on back of alternator to ignition switch; do they mean the side of the switch that's hot all the time or the side that's switchable to hot, in other words the side that goes to the coil?

 

Is it a built in regulator type? If yes, just run a small jumper (14 gauge or so) from #2 terminal where the 2 wire factory plug normally goes to the positive stud (this excites the field after fire up) and 10 gauge wire from that stud to the positive terminal on the Battery and it's done

 

Fly United yes, it has built in regulator and already has a jumper wire that came with the 2 wire factory plug, so you're saying I should wire to the positive side of the ignition switch? Thanks for responding.

 

Nothing needed to the switch. A small jumper from #2 over a few inches to the positive stud (BOTH located on the alternator), and 10 Gauge (fairly heavy) from that same stud direct to the positive terminal on the battery. That's it

 

Be sure to add a diode to that wire or it may keep on running when you turn the key off.

 

#1 does need to be fed by ignition to energize the regulator.

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Not true. I've been wiring them as I outlined for 20+ years. I currently own 2 cars wired like that. One for 10 years and the other for 6 years. I believe(?) the #1 goes to the idiot light if used

 

It goes to the idiot light or is fed by ignition but it still needs to be fed to energize the regulator. Just as the diagram that was posted shows. The alternator won't charge with just the #2 wire fed hot as the previous poster said. I respect your wiring experience but I own an auto electrical rebuilding shop and have been rebuilding for 31 years.




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Yup, you betcha, the white wire goes to the accessory side of the ignition switch, the red is the voltage regulator sensor, can be wired to the bat wire, but is better run to the power terminal of the fusebox, it'll tell the alternator more accurately how much current to put out. The white wire feeds power to the alternator when switched on, and when the engine is running will reverse the flow and go back to the ignition switch, wired to the accessory side of the switch allows the engine to be shut off.

 

Thanks everyone for the help. My alternator is a 2 wire GM 10SI with a built in regulator and was used from '73-'85. It has a DA plug on the back with a jumper wire going from #2 to the battery post on the back of the alternator; which also lets the engine shut down when I turn the key off. I now realize the #1 yellow wire on back of alternator goes to the "cold" side of my original '36 ignition switch. CONCEPT, thanks for the diagram, even I could understand it.

 

The only thing that makes any sense to me is you have probably been buying one wire alternators, cause you are not going to make a two wire work like that. Got to have a field wire that gets hot from ign. to the #1 wire on a standard alternator.

 

Actually it will work, just not in the best way.

It won't self adjust to compensate for the different draws placed upon the system by running lights or power accessories...but it will definately work as well as a 1 wire setup.
It will sense the base Alternator output and charge to match that, for want of a better description.
Most times you will need to give the car a little shot of gas to bring up the rpm for a sec so the alternator will start charging though...but thats no biggie.

My T runs it like that right now and all the engine swapped cars I built in the past ran the same way.
A Landcruiser I'm finishing off now, with upgraded and additional lighting etc, uses a version of the system pictured by ConceptVehicleDesign, because the extra demands placed on the system requires more than a basic run/charge mode.

Moving the pickup site of the #2 wire back to a main distribution point allows the "sense" wire to sense the draw and up the output of the Alt accordingly.
Definately better...but not 100% necessary on a simple Hot Rod with very basic electrical requirements, EG Headlights and radio.

 

I have wired several the same way Fly United and Hackerbuilt have described for over twenty years as well. Works just fine, but as Hackerbuilt mentioned, you do have to give it a bit of throttle to start the alt when you first fire up.

 

Yes, and if you have a larger Moroso reduction pulley on the alternator you have to give it a much larger blip of the throttle to see the volt meter charge

 

Well, remove the optional idiot light (I like a volt meter) portion of this diagram, isn't this now a longer version of exactly how I said to wire it? (#2 to the battery post and battery post to + on battery)

 

Yes.
The benefit of using it with the longer sense wire is you sense the voltage draw much farther out in the circuit so the alternator will up its output to compensate for the resistance to that point.
Important for a circuit with a potential for a large draw like powr windows and upgraded lighting etc.
Using the idiot light wire makes the alternator work on startup without reving the engine and obviously gives you the idiot light which can also be a good thing.

Using all wires as the General designed them is obviously the BETTER way.

 

And the "idiot" light in this case will act in place of the diode and control back feed.

 

Thinking back, I think my buddy turned me on to the way I outlined around 1994. Since then I've done it this way I can't think how many times at my shop. I've yet to see a "down" side, but I do get what you're saying. What determines length of the sense wire? How many feet/inches per....(?)

 

No idea!
My take on it is you just need to sense off the main distribution point. It's just a way to ensure you get all the power you need when you need it and where you need it.

On my T I'm pretty sure its been looped from #2 to the BAT output terminal since the car was built in the late 70's/early 80's and I see no need to change it with my minimal requirements.
Big barge with power everything...I would go with the full GM design.

 

If it was this, we wouldn't be talkin bout it here on the HAMB. LOL

 

Not always. For the times that it doesn't:

http://www.radioshack.com/product/index.jsp?productId=2062577#tabsetBasic

That's $1.99, for a 2-pack, plus a little for the man.

Put it in the 12V ignition switched lead, between the light and the alternator. The end with the stripe goes towards the alternator.

 

Pretty much why I said "in this case". The diode is a good idea but "not always" required.

 

Yup, just fliin' out the details.

 

UPDATE: Car starts now but the '36 ignition switch can't handle the load and blows the 15 amp fuse in the ignition circuit. Someone suggested I could use a relay with the ignition switch so I wouldn't have to replace it; anybody know what relay I should use and how to wire it? Am using a push/pull switch rated at 75 amps for now in place of the stock ignition switch.

 

Gimpy, thanks, that's exactly the info. I needed! Will this work?

 

The relay should handle the heavy 10 gauge load, not the switch. I think Gimpy meant to convey this. The heavy 10 gauge should only go to relay # 30/87.

<b><big>This is a typical wiring diagram for a standard relay installed for</big>
<big>headlights, horn, fuel pump, electric fan, etc. If the relay has a</big>
<big>5th terminal, it is not used.</big></b>​

​

 

Yup, just grabbed the first decent diagram I could find. That one happened to feed a fuse block.

 

I saw a recent ad for one and thought.......So, how does a one wire alternator sense draw?