older smiths tacho (again, i know...)

[Mk1Sport]

sorry i did a search but i couldnt find anythint that explains how...
on my setup the positive feed to the coil runs through the rev counter from the ignition switch, and the tacho senses the pulses from that. how wourld i get this to work?

my thinking is that...

route another wire from the ignition switch through the tacho and then to the coil-a and coil-b wires? from what i understand i have to make up that diode circuit, but without the zener???

just need someone to confirm...

thanks for bearing with me!

[fikus01]

there has been some discussion on this, some have found success without the zener diode i think, others coundnt get it to work at all! i think you'll have trouble with that type unless sum1 has a new conversion circuit that will make use of the tacho output from the megajolt!

[themaninthesuitcase]

I know 2 people running theirs off of pin 11 on the EDIS with out problems.

[MartinM]

Why not try doing exactly the same...

+12v ---- tacho ---- wasted spark coil

Most tacho problems are because they pick up from the switched side of the two coils in the pack and thus read half the rpm and you have to jump through diode circuit hoops to (try to) fix that.

On the +12v side of a wasted spark coil, the pulses in the current caused by the coil charging (which must be what the rev counter is measuring) are the same as in a single coil setup, so it might just work fine.

Report back....
Martin

[bon_corno]

Recently I bought a Smiths tachometer and I couldn't make it work in anyway. After digging up few sites, I found attached brochure which shows wiring for both positive and negative earthed impulse tachs.

Maybe it helps if yours is the same type. I didn't know impulse tachs before and I was thinking that mine was broken. It worked great during my bench test.

Ibrahim