Alternator check on 71 RR

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08-29-2011, 06:34 AM

Moss

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Alternator check on 71 RR

Can you check the alternator charging directly at the alternator. Mine has 2 fields and one output. Trying to see if its regulator or alternator or both.

71 roadrunner Thanks

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08-29-2011, 07:44 AM

440roadrunner

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I assume you are saying that it's not charging at all

Here's a simplified diagram:

Find the top of the ballast resistor. What you have is the "dark blue" so called "ignition run" or "ign 1" coming from the key feeds the ignition, taps off and goes to the "ign" terminal of the regulator, and either one of the push on field terminals.

The "F" terminal of the regulator (green) goes to the remaining field push-on terminal of the alternator

For quick checks, first make sure that you have "juice" to the field. With the key in "run" and the engine off, check the voltage at the "big stud" on the alternator, should be "same as battery."

Next check the BLUE wire going to one field. If you cannot get a probe on there, simply pull both field wires off and REVERSE them, then check the blue. Should also be close to "battery" voltage.

If that seems OK, next take a clip lead, remove the GREEN wire at the alternator, and hook a clip to the exposed alternator terminal. With the key still in "run" hook the clip lead to ground. You should see a small spark indicating the field is drawing current.

Next start the car and slowly bring up RPM while watching the ammeter. If you start to see a charge, and bring up RPM, you should see more. If not, take your meter and probe the "big stud" on the alternator, and again bring up RPM and see if the voltage comes up

If you see a charge on the ammeter, this much is OK and you have a problem in the regulator circuit

If you don't see a charge on the meter, but the voltage at the stud goes way up, you have a problem in the ammeter circuit, most probably right at the bulkhead connector OR right at the ammeter

If you see a charge, next hook everything back up "normal" and go up and unhook the regulator plug. With the key in "run", engine off, make sure you show voltage at BOTH terminals at the regulator plug. Next "rig" some nails or meter probes, etc, into the regulator plug and jumper the two together.

Once more, start the engine and see if the ammeter shows a charge

If it does, replace the regulator

If it does not, and the previous alternator check was OK, you have a wiring problem in the regulator circuit.

Post back

EDIT Don't know what happened to my post, I attempted to post a photo and "this" happened.

Last edited by 440roadrunner; 08-29-2011 at 07:47 AM.

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08-29-2011, 12:22 PM

Moss

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Nice job of explaining this by using the amp gauge itself. I will give it a shot. Thanks!

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