Turkey Rod Runs are this week so I was taking the fastback out for a shakedown cruise and everything was going great until...

Less than 12v on the voltmeter so obviously the charging system was not doing its job. Is it the alternator? Voltage regulator? What?

It has been a while since I have had to mess with the charging system but dipping into my way back memory I recalled the test an old Wrench showed me years ago and since there are a lot of Classic Mustang newbies around, I figured this might be useful to some.

1) On the back of the alternator, take a jumper with alligator clips and clip the Field and the Battery posts together. Use a mirror and you will see "FLD" cast into the alternator housing and BAT will be cast on the other post.

2) Start the car. If the system starts charging up then your alternator is good and your regulator is bad. The system will go to full charge when this happens so don't leave the car running like this, just long enough to see what's what.

3) If, when you start the car, the system does not start charging then it's your alternator. It doesn't mean that your regulator isn't bad too, it just means that your alternator is definitely bad.

 

Accurate, or you can just short two pins together on the Vreg plug (the white and yellow wires or A and F location on the plug) and do the same thing without getting so dirty.