Sorry Colin,but my Gen set is at the boat yard. There was no AC plug on the unit, just hard wired.

If your unit is a 3CR (like 7.5 MDJE 3CR) than here's how to hook it up.

For 1 phase, 2wire, 120 volts
T1 & T3 are tied together. (Hot)
T2 & T4 are tied together. (Ground)

For 1 phase, 3 wire, 120/240 volts
T1 (Hot)
T2 & T3 are tied together. (Ground)
T4 (Hot)

For 1 phase, 2 wire, 240 volts.
T1 & T4 are tied together.
T2 (Ground)
T3 (Hot)

Note:
T2 must be grounded. Any other ground will cause serious damage to exciter.

It's been many years since I wired mine and I don't remember if the wires where marks or not. Maybe Bob can provided some more information.