Hi Laurie
There is a component connected between pin 8 (sensor signal in) and pin 3 (earth) on the plug that fits into the back of my instrument. Unfortunately I don't know what it is because it is contained within a piece of sleeving. It could well be a resistor and if that is the case it would be a 'pull down' resistor but this depends upon the type of sensor fitted. My sensor is fitted in the vehicle's gearbox, I suspect your sensor is near the front wheel hub and they may be different electrically. I have not heard of failures of this component.
I followed the cable from my sensor and it arrives at a three pin connector, hanging in the cables on the drivers side (see photo). The steering column shaft is just under my hand. The three pins carry earth, plus 12 volts with the ignition on and the third pin is the signal back from the sensor. I jacked one of the rear wheels up, monitored the voltage on the signal pin with a volt meter, got my wife to spin the rear wheel and watched the signal volts changing from high to low as the wheel rotated. You might be able to do a similar test if you can find your sensor connector but in your case it will probably be one of the front wheels. Obviously the ignition needs to be on during this test.
I have posted the details of the VDO speedo test rig within another post, see here
https://www.talkmorgan.com/ubbthrea...er-not-working-on-2008-plus-4#Post817814