There are three wires coming from the coil on my Mk1 Focus ST170 engine (running standard fuel injection with a Megasquirt ECU) sitting in my MK Indy R:

Orange and black
Green and blue
Green and black

Does anyone know what purpose in life these all have?

Thanks in advance,

Elvis

Yep, they serve the coil with info for sending volts to the spark plugs.

They are logically arranged. The zetec coil is two coils. looking at the plug on the coil the middle contact is ignition live, the left hand one fires the left coil for 1/4 and the right hand wire fires the right coil for 2/3. Wasted spark.

Thanks for the replies. More specifically which wire is the switched negative or am I missing something?

Thanks,

Elvis.

Middle one is 12v live, 1 & 3 are switched by the MS

No negatives.

[Edited on 8/8/12 by coozer]

MS switches the two outer pins to earth, these are the ones you connect to pins 32/33 & 34/35 on the MS.

If you want to drive a tachometer from a wasted spark coil like the Ford one, then you will need to add a small amount of external circuitry. Simply hooking up the tacho to one of the switched coil connections will result in the tacho reading half the engine speed.

Thanks for the responses everyone. I'm going to try a couple of things this weekend and will let you know how I get on.

Cheers,

Elvis.

Just a thought, are you using EDIS? Is the MS edis type or does it have its own coil drivers?

This turned out to be a very straightforward job:

1. Splice into the left wire for cylinders 1 & 4 and connect to the SPA Tacho.
2. The SPA gauge expects one pulse for each cylinder so I set the "Number of Cylinders" setting on the Tacho gauge to 2 rather than 4 so that it multiplies the number of pulses per sec by 2.

It took all of 5 minutes

Thanks again.