MTH 2 rail SD45 Motor Isolation?

That doesn't appear to be the factory wiring solder job. Where are you seeing the motor wires connect to? If they use the chassis for the return, you'll have to drop that.

For isolation, just run the wires directly to the decoder using the decoder's install manual.

Tony's train exchange site used to guide me on DCC installs.

The motor brushes are most certainly isolated from the the chassis or it wouldn't work in 3-rail either.

Yeap, that's what I get for assuming he's connecting his meter to the chassis of the engine.

It's fun when someone else reports a possible problem and wants a solution.

@Bruce Blackwood posted:

...my meter seems to be telling me they are not...

To be clear, your photo shows yellow and black wires coming from the RS-385PH DC can motor.  You're saying that with these 2 wires floating (not connected to any electronics), your meter indicates continuity between yellow-to-chassis and/or black-to-chassis?

You may find solder from a motor terminal is touching the motor case. That would give you the continuity reading 

Found the problem, motors are isolated from frame but not from a piece of bare wire from a trim job that found it's way between the frame and motor mount clip!  Yes, someone has been in this locomotive .... as normal with some online sales, the history of used equipment is unknown or at least, not reported. Once I get the DCC / Sound install completed I  should be happy and not so frustrated. Thanks for the suggestions and help. Bruce in Mount Airy, MD    

I had an early MTH 2-rail diesel (sold it years ago) and my recollection is that MTH used the frame as the ground and used insulated wheels on one side of each truck with wipers for the hot.