Lotus Elan and Lotus Elan Plus 2 Forums

That's clever, Bob, and a pity I don't have a dimmer anywhere. I think a headlamp bulb might swamp a cheap low-current charger, such as I'm using, and a stoplamp/flasher bulb might be enough as it's all about edge speed. Polarity is critical to operation, though not damaging, so be prepared to reverse the connection, people, and don't forget to power the tachometer independantly.

In theory you could do it in the car, and might have to on a S1 or S2 (not sure about S3) due to their non-electrical connection, by including (in the loop with the bulb) the power wire to the coil (detached) and the battery (regulator A1 perhaps or starter solenoid) and turning on the ignition to power the tach. I might be doing something like that myself if I develop my system.

Very knowledgeable group here but I imagine the Smiths S1-2 RV tach is pretty much the same as all the Smiths tach's of the period. Electronic tach design was very young then and it didn't take long before they changed their design. When new they were probably better but its been my and others experience that even if you have them calibrated correctly they are not likely to stay that way. I did not originate the idea but I would suggest drilling a hole thru the case so that you can adjust the potentiometer while the tach is fitted to the car. I've done that with one.

Kurt.

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