In 2006 OGR published an article on rewiring motors from parallel to series wiring. I have done that to a number of older diesels in my collection. Recently I came across a later issue K-Line MP-15 that had a switch on the bottom to select Series or Parallel wiring. The switch was part of the electronic reversing unit but I thought it would be a good idea if I could adapt it to my older diesels.
I determined all that was needed was a small TPDT (triple pole, double throw) switch which I was able to obtain on eBay for about $6. It took me some time to think through the wiring. I've done this on 3 older K-Line MP-15s so far and I find it very handy as you need the power of parallel wiring if pulling more cars. On K-Line the motors have blue and yellow wires while the reversing unit has a blue and brown wire. I'm attaching the wiring diagram. I had to color the yellow wires orangish to have better visibility. The switch is viewed from the bottom.
