mindless speculation
I'm not familiar with this locomotive, and have minimal DCC experience. Be warned this is pure speculation. Often times the PC board carries a plug to plug in a factory decoder , or a bypass plug, that runs the motor directly for DC operation. That way the manufacturer starts with a single product, that can then be prepared as a DCC or a pure DC product.
On the Bachman shay that we converted to DCC for use at the club, we were able to plug a decoder into the Pc board in the tender. we had to use a n scale decoder and it was a tight fit.
I have Bachman Thomas I converted to DCC for use at the club (the decoder rides in Annie). it had a PC board that was not DCC related. I left it in place, and it fried the first decoder, so I decided to remove it.
As a practical mater, if you don't have a good wiring diagram for the board, it might be safest to remove it, and run your own wiring for the DCC, and at least that way you would know for sure where each wire goes, and would gain the space, which can be critical when messing with too many wires.
Bill Nelson