On a 1994 4.0l starter motor there are only two wires
Large Red wire from battery, positive terminal.
Smaller wire from "clutch switch"/key switch
Picture here: Part 1 -How to Test the Starter Motor (Ford 4.0L)
B+ is battery cable
"S" is smaller cable
Smaller wire should only have 12volts when key is turned to START and clutch pedal is in all the way
Starter motor is Grounded by being bolted to the transmission, but the Negative battery cable(black) is sometimes located on one of the starter motor bolts that hold it to the transmission, this is done because starter motor is the biggest amp draw in the vehicle, so needs the best connection to the battery.