[Rick Becker]

Had one on my 912 for many years, hopefully you have the factory wiring diagram. I followed the diagram and made up a small circuit board so the electronic tach would operate normally. I was told later that for the Porsche tach, I could have switched the signal feed wire to another connector tab on the back of the tach and skipped the circuit board, but without documentation wasn't inclined to try that.

When you turn the ignition on, you'll hear a high-frequency sound when the unit is working properly. Mine always kept the plugs from loading up/ fouling when the engine was cold. A minimal current goes through the distributor points, resulting in minimal pitting.

The Mark 10B units do eventually fail, but can be rebuilt. If it fails, pushing the button on the Mk 10 B will turn it off, and switch the traditional ignition wiring setup back on with the original amount of current going through the points. However, it's VERY important to disconnect the electronic tach, to prevent damage to the tach until the Mark 10B is repaired and switched back on.