Cool Wiring And Rev Counter

[Guest Seanus01]

Evening,

 

I have finally got my car running and all is good with the exception of the Rev counter. I fitted all new gauges from Cbs but cannot get the Rev counter to work. Wired as per diagram with signal from negative on the coil. I have replaced the original coil and distributor with an accuspark electronic version and ditched the ecu from my original. In case the original wiring to the coil is now incorrect due to ditching the ecu, is it ok to rewire the coil fresh, removing the existing wiring and how is this done? I assume it is a negative to the chassis and switch live to the positive of the coil? Then from distributor does black go to negative and red to positive on the coil? Anyone else had this issue?

 

Thanks

[Longboarder]

It is good to rewire the coil with a clean 12v switched supply to coil positive. Not through a fuse. Make sure the coil has a resistance of greater than 1.5 - 3.0ohms across the two spade terminals.

You do not put an earth on the negative terminal of the coil! Think of it more as the signal terminal of the coil. This negative terminal is connected to the blue or black from the accuspark dizzy. The (usually) green wire to the rev counter also connects to the negative terminal of the coil.

The red wire on the distributor also needs a 12v positive switched supply.

All these wires are best done with fresh wires. Isolate and tape off the old wires that were used by the old ECU.

 

Nigel

Edited April 22, 2016 by Longboarder

[PaulF2B]

I previously had a regular points setup where the coil negative is connected to ground 2 times each revolution of the engine.

The sierra rev counter connected to the coil negative would then get the pulses and convert this into RPM.

There are 2 pulses (sparks) per crank revolution on a 4 stroke engine, you will notice you have to turn the crank round twice for 1 rev' of the camshaft and all 4 pots to fire.

 

I then fitted a Powerspark electronic ignition module, but with the rev counter fitted it added extra electrical loading to the coil negative (it's impedance was too low), and the engine would not run smoothly, missing some sparks.

 

A better solution for the electronic ignition modules is to get the rev pulses from the alternator. If your alternator has a "W" terminal you should be able to connect this to the rev' counter feed and keeping the coil connections to the minimum.

[Guest Seanus01]

Thanks for the info, have retired all fresh and car runs fine, Rev counter operates but fluctuates quite bad. Will look to see if I can pock this up from the alternator. Could possibly due to a faulty gauge perhaps as I had previously wired wrong and had a permanent 12V supply down the signal terminal