GM 3 wire alternator repair

I own 2 tractors, bull dozer , compressors, a model AA swamp buggy and I installed 3 wire GM alternators on them, they are known as model 10 SI made from about 73 to 83, I like them because I dont have to rev the engines to 2000 rpm's to make them charge. I have other equipment that I would like to install the same type alternator on them. I've been given several other 3 wire GM alternators but they dont charge. I can take them apart and change the brushes and turn down the slip rings in my lathe. I would like to know how the check the other internal parts like the diodes and the internal regulator, I have a multimeter with a digital readout. I tried to find info on the web but had no luck.
Hope you can help, thanks nick c

 

Unless you have a very early one that had "F" and "S" by the slot in the case for the plug in terminal there should be a "1" & "2" beside the slot. On low rpm equipment you probably just have a jumper from the "BAT" terminal on the back of the case to the number 2 terminal. If you make a momentary switch from any 12v source (except the coil wire) to the number 1 terminal it will excite the alternator at any rpm and it will stay that way until the engine is turned off. I like to use an all weather tractor or boat starter button since equipment is often out in the rain. Diodes are checked with a test light and a jumper; 12v positive jumper to diode can and test light to diode wire and neg battery. Now 12v negative jumper to can and test light to diode wire and pos battery. If no light either way it's bad; if light both ways it's bad; if light one way but not the other it's good.

 

you can use an ohm meter to check diodes, they should conduct one way, but not the other way. Testing the regulator is a bit difficult, they either work or they don't.