Ok, so a few updates. Yes, I'm getting a voltmeter. But I'm not sure that'll help.
No one in town was willing to test either the board or the motor. Except a nice RC shop dude, but the connection was a bit different so he backed out.
Anyway, I decided to use my brains for a bit and realized the MOMO and the DFGT have the same ffb motor. So... I popped open my old and faulty MOMO and decided to swap motors.
Results: both motors work fine when plugged on the MOMO. Both motors work REALLY SLOW AND UNPOWERED when plugged into the DFGT. They turn reeeeally slowly and have barely any power. If I just hold them with my fingers they stop and that's it.
So. I think we can rule out the fuse problem it seems. If a fuse had popped no current at all would go through. Right? We can also rule out the motor, as it spins nicely when plugged to the MOMO.
What else could it be? Just something wrong with the circuit board, I can't think of nothing else. In all this disassembling and assembling back I think I'd have found a loose cable connection by now if that was the problem.
One last symptom: the steering on the DFGT is dead. Oddly enough, when the problem started, the steering kept working. However, after turning the computer off and on again, no more steering at all. I've tried with both the motor plugged and unplugged, and with the MOMO motor on, no steering. All other buttons work.
And one last thing: I have bought a faulty DFGT for myself, in an attempt to make two out of one. But I don't know which one of these to get:
1) powers up, calibrates to the right and then full left and stops then keeps doing that over and over again.
2) when plugged in the GT light just flashes, nothing else.
If the problem was the motor I'd go with #1 of course. But now that the problem seems to be on the board... I'm lost. And lonely, and sad. And I feel bad for hijacking this thread now.
Thanks.