Fuel injector harness Part number AMR6103 fits to the Defender and the Discovery 2 with the TD5 engine. This wiring harness is the source of a common problem. Check your ECU red plug under the seat box for oil ingress.
If your TD5 engine is misfiring or has engine management problems it is very likely that oil has found its way into the harness from the engine.
The harness will need to be replaced and any oil will need to be cleaned out of the ECU plug and sometimes the ECU itself.