HEAD-HYD CYL-YM 3831591 - Caterpillar

Service Magazine, SEBD1672 July 1986, "Brushless Alternators May Not Charge In Certain Conditions"
Start the engine and set the throttle to at least 75%.
Connect a voltmeter between the "B+" terminal and the alternator case ground.
If a wire is connected, disconnect the wire from the "R" terminal.Expected Result: The voltage does not change.Results:
YES - The voltage stays the same. Continue to Step 4.
NO - The voltage rises and the alternator begins charging. The wire to the "R" terminal is shorted. Repair the wiring or replace the wiring. Go to Troubleshooting, "Initial Troubleshooting Procedure" and retest the system.
Connect one end of a jumper wire to the "B+" terminal of the alternator.
Connect the other end of the jumper wire to the "R" terminal of the alternator for two seconds.Expected Result: The voltage output rises on the "B+" terminal.Results:
YES - The voltage output rises. The alternator is now charging. Go to Troubleshooting, "Initial Troubleshooting Procedure" and retest the system.
NO - The voltage output does not rise. Repair the alternator or replace the alternator.