Since this model is already wired for DCC operation, no work is required on the engine. Sockets allow the engine to be unplugged and safely stored while all conversion work is performed in the tender.
Clearing space in the tender
Removing 2 screws allows tender body and chassis to be separated, providing access to a circuit board that terminates engine connection wires and includes an 8-pin decoder socket.
There's no wiring diagram for this loco, but the circuit board gives enough clues to figure out which wires are motor, headlight and rail pickup connections. Engine connection wires are the only items reused in our conversion. Everything is removed from the tender and all mounting posts, etc. are cut from the chassis to give a flat unobstructed surface.
Arranging radio control components
Not visible in the figure is a styrene bracket to hold the battery and support vertical mounting of decoder and radio receiver each side of the battery. I've departed here from the usual arrangement of mounting decoder and radio receiver back-to-back.
Installing battery power components
With minor trimming and removal of battery socket, the BPS board fits neatly in the oil bunker. Battery leads are soldered directly to BPS board. Styrene bits hold BPS securely. This location has two benefits: The magnetic sensor is flush against top of the oil bunker where it's easily actuated with a magnetic wand. It's also well-removed from the speaker, which has a strong magnet. Since there's very little clearance between top of battery and BPS board, wiring must be as short as possible, but not so short it prevents opening the tender.
As mentioned earlier, a standard BPS 850 mAh battery sits above the speaker and avoids use of stiff battery leads, which are impossible in this confined space. The short connections to left and right upper terminals of the wiring panel are easily unsoldered so the battery can be removed without disturbing any other components
Bachmann's design, with tender body swinging upward on rear edge plastic tabs, helps estimate length of BPS connecting wires. When tipped to about 30 degrees, body lifts off the chassis. The tender's removable front panel makes soldering BPS connections feasible by tilting body on it's tabs as photographed left. Looking carefully, wires are visible with soldered loops prepared ready for final terminal connections.