slight update for those that haven't lost the will to live.
I can't locate the resistor but having disconnected the ECU and located the orange/black wire at the ECU connector end I get a reading close to zero ohms on a DVM. This must mean that there is either a direct to earth connection or the resistor has failed as short circuit.
Given that every failed resistor I've encountered before this one has failed open circuit I con only assume there is no resistor or there's a short to earth in the circuit. As I've ordered 5 x 510 ohm resistors I intend to cut the wire and make my own connection to earth via the resistor
Now I'm wondering if there's another orange/black wire for something else - unlikely I think
