GM Alternator to Ford

EOD Guy said:

The exiter wire #1 terminal doen't need any resistor to compensate for the light bulb......
The bulb is just an idiot light....

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OK, for the electrically challenged among us, a bulb IS a resistor. That's why the filament heats up and glows when you flow current through it. That's also why when you wire bulbs in series, they get progressively dimmer as you add more.

The exciter circuit for the SI-family alternators uses the bulb just like the ballast resistor in a point-style ignition system. Will the circuit work if you just wire it straight to +12V? Sure. Will you shorten the life of your points or electronic voltage regulator if you do? Probably. Your call.

Note that NAPA doesn't waste warehouse space stocking two different kinds of alternator jumper harnesses (one with the resistor, one without) just because they want to, and GM doens't waste money putting resistors in the exciter wire on cars that use a voltmeter instead of a bulb.

OK I'm no electronic engineer....... but I do know that when you order a re-wire kit some do not have the idiot light wired in..... it's a straight 12v switched wire, no diode, no light just a straight wire....... When I called and asked an engineer.....well .... my view on the idiot light changed........

I agree a bulb creates resistance......but I don't think I agree with your example of a ballast resistor being like a light bulb....... the ballast resistor which actually steps down the voltage so you won't burn up the points or coil........ I do not believe GM would use a light bulb to drop the voltage not to burn up an alt.... and it would be far cheaper for GM to add a resistance wire in the design vs the bulb, socket etc.....

as far a NAPA goes and shelf space....... really .... if you will buy it they will sell it.

like you said..... your call

For the OP..... here's some 130 alt wire ups

The light bulb used in the CS series alternators does the same thing as a ballast resistor. Try this test. Connect one lead of a bulb to the battery and the other to ground. Measure the amount of current flowing through the bulb. This is the maximum current that will flow through this bulb. When this lead is connected to the alternator, no more current can flow than was first measured. The alternator can not pull any more current than this. Even if it shorts out, the bulb will not flow any more current than it did when it was grounded. Many manufacturers have used this circuit, because they get both a warning light and current limiter for the price of one.

Back to the original problem. If you've got a 89 Ranger with a 94 harness and a Chevy motor, you've got a lot of work to do getting all the gauges, sensors, and ignition to work. The alternator might be the easy part.

joe_padavano said:

Just to clarify slightly, if you are not using an alternator idiot light, the #1 terminal needs about a 35 ohm resistor between the alternator and the switched +12v source. That's about the resistance provided by the GEN bulb on GM cars. NAPA actually sells a short jumper harness with the resistor built in.

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AD-1214

Is this what you are talking about here?
After having worked for NAPA for about 15 years, I can honestly say that I don't recall ever selling one of these.

They DO stock 10 of them in the Calgary DC, however ... so someone must be buying them.

Olds is a rural area, and there has to be thousands of old tractors and other peices of equipment running around here that have had a 10SI alternator retrofitted (polite term for "farmer-fix") onto them, using only one of these.

VRC-148


... wired just like this ...