taco stopped working

hi there,
had recent electrical work done on the dizzy, electrician disconnected the original wires to the dizzy and taped them all up.
not to be used any more!
now the rev counter is not working, so logic dictates that possibly one of the taped up wires, made the rev counter work?
wiring diagram too faint and small to follow , any ideas if the electrics works off the coil?


Active Member
In a word ,Yes. The tacho. uses the pulses created by the contact breaker switching to operate. I believe there are two version , exact details of your engine would help.


Well-Known Member
Just swapped out an RVC for an RVI tachometer for the usual electronic ignition reason. The tacho is on a separate loom in the S1 anyway. The RVI has two signal wires white/black and white/yellow as well as power which is fused (green). You simply tie back and isolate the white/yellow as you don't need it for RVC.

In the S1 there is also ground (black) and illumination (red/white) which is joined into the main loom. For the S2, ground is to the binnacle itself, so no wire and the illumination is also internal.

It's important that you use the correct order. i.e. it is definitely white/black and not black/white as it is a white wire with black stripe/tracer. In the Lucas wiring code, the other way around is a very different function in our case it's the brake warning light.

A truly excellent reference is here: Lucas Wiring Colour Guide : How-To Library : The MG Experience

The system worked really well for decades until cars became a bit more complicated electrically.
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