Hi Don
Your loco is 2 rails DC
So to convert it into 3 rails you need to change the wiring
- MTC 21 Pin 22 was track right now is connected to slider
- MTC 21 Pin 21 was track left now connected to both track left and track right


ATTENTION: the figure above is misleading: PIN 20 is ONLY the common return for digital fonctions AND NOT the frame ground.
Installing an mLD3 decoder, your loco is now 3 rails analog and digital
ATTENTION: double-check the wiring before applying power
Cheers
Jean

Well, that worked out just great. As I said, I had the slider in my parts bin, and I invested in a low cost Lokpilot basic DCC decoder ($35.00 CDN). At that price, I decided not to steal one from one of my other locomotives.
I utilized the rear bogie DC wheel pick up and simply unsoldered It's red wire from the circuitboard and soldered it to the grounding lug on the bogie with the brown wire.
I plugged in the three rail slider in the front bogie, and plugged in the Lokpilot decoder.
Very simple. After the third attempt at automatic motor calibration, it now drives perfectly as expected.
My total cost for the new locomotive ( Trix all-metal quality) plus the decoder works out to about the same cost to me (in Canada) of a similar new Piko hobby model, in plastic.
As you will see in the photo, like other countries, my imaginary country has recently increased its military spending.

Cheers!