Look at the solder pads... 2 are connected to ground, 2 are connected to the hybrid.
If you read the manual it tells you to jumper those if you do not have coin counters installed in the cab. If you don't have coin counters and you don't have jumpers then it won't recognize coin inputs.
Thanks, I had read the manual but was curious if there were more jumper combinations than it described - in the past I've read messages (and seen pictures) containing some strange configs where they've not been jumpered at all, some where they've been linked together (but not grounded), etc.