I have an MK Indy R with an ST170 engine which I've just replaced the dash and dials using 3 SPA gauges. The last piece of the puzzle is to get a reading for the tacho which ideally is from the ECU tacho output (ECU is essentially a Megasquirt V1.3) but I haven't a clue if that exists or alternatively the -ve connection from ignition coil. Does anyone know how to determine which wire is the -ve connection from the coil or how to determine if there is an output from the ECU??

I'll post photos of the new dash asap as I'm rather proud

I'll be even happier when I have a working rev counter though!

Thanks in advance,

Elvis.

Unless the mega squirt was ordered with a tacho output then it will not have one by default, you need some mods to the PCB and an output driver circuit building to match the output voltage to a level that will drive the tacho.To use the coil to drive the tacho you will need to connect to both sides -ve of the coil pack using a simple diode circuit, I have seen these available ready built on one of the mega squirt sites recently but cant remember which one.If you are using an Edis unit then you could take a tacho signal from that.
Paul

I've spoken to the manufacturer of the gauge and they tell me that I just need to splice into the switched side of the coil. The trouble is, I don't know which wire it is! There are three coming from the coil:

Orange and black
Green and blue
Green and black

Does anyone know what purpose in life these all have?

I can post a photo later if this will help.

Thanks.