Hello,

Here's an interesting one for you. I recently bought into the world of Datsun, a nice orange 1200 coupe and the tach wasn't working but it came with a replacement. I put the replacement in with no joy, still no tach action. So then I pulled the wiring loom apart and checked all the connections with everything going where it should. So then I thought I'd plug the tach in directly before the coil and start the engine and here it works.

The car has a performance coil and a wire wound ballast resistor on it and I can only guess that there is enough inductance in the ballast resistor to filter or smooth the current pulses through the rest of the loom enough that the tach doesn't pick it up. It's definately the ballast resitor since the tach works when plugged in after it but not before it. SO if anyone else out there is having a similar problem I hope this helps.

I can see a few solutions, use a few carbon film resistors to match wattage and resistance spec. and hope the inductance is low enough that it works. Use a high energy ignition that doesn't require a ballast resistor. Move the ballast resistor in before the tach and finally run two new wires back to the tach from the coil. I'm going for the carbon film resistors for now, 7x 10R 1W resistors in parallel gets real close to the 1R5 wire wond job. At 44 cents for two it's a pretty cheap fix. I'll let you all know how it goes.

If anyone else has been here maybe you'll have some advise or pick up on something I've missed.