I have a 24 volt generator on my d-4 that does not charge, have not removed it yet. My question is where is the best place to find parts? Cat dealer will be very expensive.

I,d check with a repair shop that does generators and alternators as they should have parts or culd get them for you.We took our generators from the Cat dealer I worked for to our local repair shop and had them repair them when I was working yet but I believe today the dealer has their own centrally located shop for the other branches to send them to.

Have you done some trouble shooting while it is still on the machine?

First one is to check all the wires from the regulator and battery.
Battery + post or starter solenoid terminal to ammeter (could be a circuit breaker in this wire),
ammeter to regulator BAT terminal
A1 regulator terminal to A1 generator terminal
F regulator to generator F
A2 regulator terminal to A2 generator terminal (this is grounded at the regulator)

Next check for battery voltage at the BAT terminal of the regulator where the heavy output wire goes out (to the ammeter usually). Also check from BAT to the A2 terminal for battery voltage, should have battery voltage at both connections since A2 is grounded. If you don't have it there, check the battery positive post to the tractor frame at the battery. Nothing again, you have an open battery disconnect switch or a bad connection somewhere or dead batteries.

If you have battery voltage at the BAT terminal, then polarize the generator by shorting from BAT to A1 terminal just to make a spark, then run the engine at high idle speed and check the voltage on both BAT and A1 terminals. Should be the same, if not, is A1 higher than BAT? what is the voltage?

If you have good charging voltage (>27 volts) at A1, but only battery voltage at BAT, then the cutout isn't closing. That set of contacts could need cleaning or adjusting the tension of the spring so that as you idle the engine up and output voltage on A1 rises above about 25 volts, the cutout will close and send the charge to the battery. The cutout relay contacts open as the generator output drops below charging voltage so that the generator doesn't drain the battery when the engine is idling too slow or is stopped completely.

If no voltage on A1, short F to ground at the frame or A2 momentarily and watch the voltage. If it generates while you are shorting the field terminal, then you probably just need a regulator or cleaning and adjusting the regulator contacts of the one you have.

I have had pretty good luck cleaning the contacts with fine sandpaper and then polishing the contacts with a clean piece of card stock or white paper

If the generator won't generate even with the F terminal shorted to ground, then check the brushes and commutator. Brushes should be free in the guides and the commutator they run on needs to be clean. It can be blackened from the brushes, but shouldn't show any corrosion or damage from arcing.

Or just remove both regulator and generator and take to the generator and starter shop!

Good luck!

Thanks for all the info. on trouble shooting. I have rebuilt several Delco starters and alternator; but due to my age 32, genarators were old tech when I went to school. I would have just replaced the regulator and cleaned/repaired genarator. It is nice to have a clue on the wires.
Thanks again for the advice, Chris