James,
look in the heavy maintenance manual in chapter 74-00-00, section 3.13 wiring diagrams. fig. 74-19 is for older engines with a separate grounding wire plug. fig. 74-20 is for newer engines with the grounding wire in the module plug.
If yours is the newer type, unplug the large module plug which connects each module to the alternator. Place your mag switches in the OFF position. Touch the multimeter to the BROWN wire terminal in the plug half that goes to the alternator. (I think that is the male plug). Touch the other multimeter lead to ground anywhere on the engine block. With the mag switch in the OFF position, you should read a completed circuit. With the mag switch in the ON or RUN position, you should read an open circuit. That will tell you if the problem is in the mag switches or switch wiring. That is where it usually is.
If you have the older wiring setup, there will be a single pin plug just for the brown ground wire but the check is done the same way.
Bill.
