Testing Generators on the Vehicle or Tractor, Part 1

Testing 'A' circuit generators are pretty easy.  First, disconnect the 'F' terminal either at the generator or the regulator.  You must do this to prevent damaging the regulator if it is still good.  Start the engine and have someone watch the ammeter (which is the gauge that should be being used with a generator) and then use a jumper wire and ground the 'F' terminal on the generator.  If the generator is good, it will go into full charge instantly and show that way on the meter.  What ever you do, don't touch the 'F' terminal on the regulator when you do this.

If the generator does go into full charge then it is probably good.  So after you reconnect the 'F' wire, if it doesn't charge then the problem is probably the regulator and will need replaced.  You could also remove the regulator's cap and try to clean the contacts to see if it will work.  Also make sure the regulator has a good ground as that will also cause it to not work.

One last thing you can try, is to re-polarize the regulator.  This has never worked for me, as my problems have always been elsewhere, but it's worth a try.  To polarize the regulator on an 'A' circuit system, With the engine off and everything connected including the battery, (positive or negative ground) take a jumper wire and momentarily touch the regulators 'BAT' terminal to the 'ARM' (or 'GEN' terminal, which ever way it is marked).  Only hold the wire on it for a second and them remove it.  It will spark when removing it and that is normal.  If there is no spark, check the wiring to make sure you have battery juice to the 'BAT' terminal by checking it with a test light or meter.  Once again, DO NOT touch the 'F' terminal or it will instantly fry the regulator.  (My directions for polarization are only general and you should follow the directions you receive with the new regulator if they differ from what I have stated here!)

On some regulators the 'ARM' terminal is in back or underneath and may be hard to access.  In that case you can jump from the 'BAT' to the 'A' terminal on the generator as the wire from the 'ARM' terminal goes directly to the 'A' terminal. 

One final thought today, most regulators used with 'A' circuit Delco generators have either three or four terminals.  The three terminal units terminals will be marked 'BAT', 'ARM' (or 'GEN') and 'F'.  Four terminal units are marked 'L', 'BAT', 'F' and the terminal in back or on bottom 'ARM'.  The 'L' terminal on the four terminal unit, if used, is for the vehicle's or tractor's lights and is usually wired directly to the light switch.

I will cover 'B' circuit generators in the next post.