A, its really the Sanwa RECEIVER thats the problem.
If nobody comes up with a sensible suggestion, my way, apart from goggling a lot for official Sanwa information, would be to open the RX case, and look for an electrolytic capacitor (one of those probably pale blue little dustbins), see which connection was -ve, and chase the track back to the pins. Or look at the I/C number, goggle for its datasheet to tell me which pin was ground, and chase the printed circuit tracks back from that.
One row of pins will be the common ground, the other common one has got to be +ve, which leaves the signals being the one thats left. This can be double checked by chasing those tracks and seeing them go all over the place.