Is there any good method of testing a suspected DC motor failure in the field using basic test equipment such as multi meter,amp clamp and megger? Also how does carbon build up cause low meg readings and does this test really tell you anything because of the influance of the carbon on your reading.
I guess what I am asking is there any easy fail safe way of testing the field,series and armature circuits of a DC motor?

And what is the proper way of changing rotation on a dc motor, swapping fields or armature leads,I have seen it done both ways?
Thankx Bean