RPM/tach signal wire

[TonyS9]

The voltage is the back emf from the coil primary, probably more than 25V (or -25 maybe). You'll not have much accuracy trying to measure a pulsed signal on a dc meter.

There is a 5v rpm signal between the ignition and fuel ecu, and this can be converted into the required level with a relay coil and transistor. You have to do this for wasted spark mods typically.

[aardvarkash10]

Originally Posted by TonyS9

The voltage is the back emf from the coil primary, probably more than 25V (or -25 maybe). You'll not have much accuracy trying to measure a pulsed signal on a dc meter.

There is a 5v rpm signal between the ignition and fuel ecu, and this can be converted into the required level with a relay coil and transistor.

or, hey, just put a dual spade terminal on the coil -ve and run a wire into the cabin...

[Mattty]

Originally Posted by aardvarkash10

or, hey, just put a dual spade terminal on the coil -ve and run a wire into the cabin...

Ah, I didn't know I could do that, might give that a go instead as I'm having trouble getting the shift light to work and not sure if its just a faulty product or not... Thankyou!

[Laird Scooby]

Originally Posted by Mattty

Ah, I didn't know I could do that, might give that a go instead as I'm having trouble getting the shift light to work and not sure if its just a faulty product or not... Thankyou!

You mean there was nothing in the sintructions about picking up the tacho trigger signal from the -ve terminal of the coil?

I suppose they've designed and written the instruction manual for the new generation of cars with one coil pack per plug, all individually controlled, timed and triggered by the ECU which somewhere along the lines will still have a timing sensor that would generate a signal.

Good job you don't have contact breaker ignition and no tachometer, you'd have really been in the dark about it!