Electronics - tacho 4/6/8 cyl selection switch replacement

No sparkies aboard?

Because the test bench can be used for different engines, I'll use it mostly for Ford Cologne V4s and V6s.

Strictly speaking I don't need an engine test bench, it's just a hobby project and making it the way I want it is part of the fun. Can't get a hand around the back, there is a panel that holds some parts. I'll order a pointy tip for my soldering iron, de-solder the switch and see what the multimeter says; all I can see now is that all 8 pins are soldered to the PCB. Should I mess up the switch/ gauge I'll buy a new one, it was less than 11 quid delivered.

Thanks for the tip, but I think moving the switch should be easier to be honest.

A 2P3T switch was likely the most cost effective option for the designer. They didn't need two poles, so each pair is connected together. They could have just as reasonably left the other half not connected.

Yes. You could have used four thin wires.

From the left, you have: position 1 - (gap) - common - position 2 - position 3.

Assuming this is a 4 pole 3 throw with an outer ring of 12 pins and an inner ring of 4 pins, looking from the back connect common to one of the inner ring (doesn't matter which one), and the corresponding three pins in the outer ring nearest it are position 3 - position 2 - position 1.

You can see here, the switch is selecting between three resistances and they've handily marked on the PCB what they are: 33kΩ, 22kΩ and the leftmost one is two 33kΩ in parallel, giving 16.5kΩ. With values that high, there's almost no current at all so wire thickness won't be an issue. You might find that having a run of cables makes the device susceptible to picking up interference, e.g. when the engine's running. If so, you could try drilling the bundle of wires (i.e. twisting them together using a drill), and if that doesn't solve it then try using screened microphone cable like you sometimes see used on crank sensors.