Tachometer wiring puzzle

[Donels]

My 1972 +2 was purchased as an abandoned project. It’s part way through a complete restoration and I’m just reassembling the dashboard, however, I have a problem with the tacho wiring. The engine had been fitted with EFI which had been removed but the wiring seems to have been modified to suit EFI. See following pics taken during stripdown.

The white wire from the coil appears to have been disconnected and a new short harness with a red and a ‘white’ wire added. Presumably this went to the EFI system.

The tacho has also been modified to suit. Can I use the tacho and if so how do I wire it?


Dave

[HCA]

Have you not tried asking Vintage Restorations - you have a job number on the label. They might have records still.

Two ways to drive an old tacho with EFI, buy a driver to convert the ECU square wave or have the tacho converted to receive the square wave. You may well have the latter. I do not know if there is a driver to convert voltage to square wave.

[mbell]

If needed you might be able to hook it up to something like a permatex rev limiter that has ecu style output.

https://pertronixbrands.com/products/pe ... ev-limiter

[Donels]

Good idea Hal. I have emailed Vintage Restorations. I suspect that red wire is power from ignition switch, white wire is negative to coil and black is to earth. Let's see what they say.

[HCA]

But you say the Tacho ‘has been converted’, so be prepared for a reply that says the white wite is to an ECU tacho outpout eg pin 12 on an Emerald…

[Donels]

I got a quick response from Vintage Restorations saying the tacho was modified to work with Motec fuel injection but it was done by Speedy Cables and they were just the postbox.

Speedy Cables were less than helpful, surprisingly, so I took it apart myself and have ordered a Clocks4Classics circuit board and will bypass the Speedy Cables circuit board.

Dave