Joe, you didn't mention what year your 140 is. but on my '71 140 the voltage regulator is a finned affair on the left side of the pedestal. It should have 3 wires going to it. The two outside wires are AC from the stator, and the inside wire is DC, with the tractor frame being the other side of the circuit.
With the engine running at half throttle, you should be seeing around 13 volts at the battery. You should read the battery voltage with the engine not running, then again with it running at half throttle. You should be seeing higher voltage with the engine running. If not, then some trouble shooting is in order.
Let us know what you're seeing, and we'll trouble shoot from there.
Steve