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Anyone happen to know which pin is which on the VDO tachometer?

Mine is reading low, and I found that only two wires are hooked up. The terminal closest to the drivers side is connected to ground. The next one is connected via a resistor (in white heatshrink) to the coil, and the third one is not connected. I assume that the resistor should be used in series with the 24V connection to drop the volts down to 12V, so a previous owner presumably hooked this up wrong by putting it on the sensor line to the coil. I put an oscilloscope on that line, and I have a nice square wave on it that goes up and down with engine revs.

I assume that the gauge is being powered (not very well) via the internal clamping diodes on the input, and that is why it works at all. But I bet it would work a lot better if I actually connected 12V to it. Which terminal would that be? Presumably the third one, closest to the passenger side?

Any info greatly appreciated,
Richard

Richard
Just happen to have this info on hand.

Going from left to right looking at the bottom (from the back) of the guage we have thus:-#2 IS SENSOR, Middle connector is +Ve and has the resistor, and lastly the other connector is -Ve or ground know as "earth" in the hallowed isle. Remember the sensor MUST be connected to +Ve at the coil. That maybe your area of concern reading your post--OR that the coil is hooked up backwards.
Hope that helps
Dennis

Thanks Dennis. That's exactly what I needed to know.

Mine is hooked up wrong, as I thought. Easy to fix in the morning.

No problem decoding your English (being from Belfast myself).

Many thanks for the quick reply.