I just finished doing a complete WD board set, I'll be posting a few in the for-sale forum soon.
Here's the "kit" contents, the DCS Remote Commander logic board, the JWA WD Generator board, and some mounting standoffs and screws to mount the board in a convenient place.
The board has some screw terminals to connect it to the output of the TIU channel, the black input jack is not used. The size wire is totally noncritical, you can use any gauge wire you have around, even as small as #28. It's just a signal that comes out the connection, no significant current.
I tried to make sure folks knew which post goes to the center rail, can you see it?
Here's the board with the WD generator installed.