MTH PS2 allegheny schematic wire harness pcb w/2diodes

The two diodes have their anode facing the motor and the cathodes (stripe) tied together and connected to the PV (purple) wires in the harness.  For many installations, I have to remove the diodes and hand wire them to make the tether jack fit in the space in the locomotive.

You can still get the 10-pin tether connection board without the diodes, MTH AG-0000039.

Thanks for answering my question  But I am confused. The 2  diodes w/ the cathodes (stripes) are on the left side  looking from the rear of the engine looking toward the front.There are 2 pins at each end.  The pins on the anode end don't seen to have any connection to to a trace,unless it was cut off, Shouldn't there be one, The pins on the  cathodes end have the two purple wires and the two pins soldered together. I get nothing. no chuff or headlight The engines runs I get start up sounds, fan works smoke elements get hot  But no chuff.   Do the purple wires power the chuff & headlight?  And is there a connection that I'm missing.

If the anodes (the end without a stripe) don't connect to anything, I can assure you that stuff won't work right.   The purple wires internally connect to the cathodes of the diodes (the end with a stripe), and create the PV voltage for the locomotive functions.  If the anodes aren't connected, you won't have smoke or a headlight.

Now, if you have a locomotive with a mux board, that changes things.  The diodes are on the mux board and not on the connector.

It's neat to keep guessing what you have, but maybe you can give us the actual model number...