There have been various warning, mainly from TVR owners, of poor quality rotor arms, so a new rotor arm may not be rock solid. My memory is that there was a thread or two about it on the TVR forum on Piston Heads, I did buy some from one of the recommended suppliers.
The connection between Morgan loom and Land Rover engine loom is under the dash, to the far right side, I forget the number of pins, but I think that there are 7 wires connected on the LR side, my notes of the wire colours are as follows
white/slate ignition
white/pink fuel pump
black/yellow mil light (not used, not wired)
yellow speed sensor
brown battery +12v
orange/black neutral switch - not used, can't remember if it is wired to 0v
pink/yellow heated screen (not used)
The MIL light is inhibited in the ECU program. What may look like a MIL light on the dash lights up when the inertia switch is activated.