I guess it is in parallel with the charge warning light which is probably an LED. So it will pass current when the engine is not running to excite the alternator and when the engine is running, any small current still being drawn by the alternator will not be enough to drop enough voltage across the resistor to produce the forward voltage required by the LED, stopping it from glowing dimly. Well done. Miraculously, and as usual, the diagram makes sense immediately and after the answer is known. Sort of. Tacho: The resistor has a wire labelled 177. There's a two-way something labelled G 171, NY 152. NY is the traditional colour for charge warning light. There's NY 177 on the tacho connector. There's NY 152 on the dash side of the main connector which comes out at NY 62 on the engine side. There's NY 62 and at the alternator. The alternator is of a type that doesn't have a separate exciter. Speedo: Similarly with YB 157, YB 178, YB 156, YB 54, and YB 155 on the vehicle speed sensor circuit of the chassis harness. But also pin 27 of the PCM. Does the resistor in this circuit then modulate the speed signal in some way? I've written those as statements rather than questions to make it easier to read. Please check. All corrections welcome. Jonathan