Okay, so after reading through the Trooper manual, (which I found on a Jeep site) it turns out that even the '98 RHD Trooper has the same colour scheme as the US Vehicross. What I DID find very helpful was the TOD error codes and reset procedure when you don't have a Tech2 diagnostic "reader".
Following the instruction, pin 8 to earth and ignition on, it pulsed codes 13, 28 and 32. All related to wires going to earth, or off. Now I'll need some daylight time at home to track and replace those wires.
Pin 8 to earth, ignition on, T/C in neutral and pulse the brakes 5 times in 5 seconds works well for resetting the error codes.