Piranha Brother 2 said:
Thanks Cam. Good to know. So ... when I finally connect it, I need to locate the input wire on the tacho correctly. I think there are numbers for each input. Is there a way of determining what's what (generally)?
On the Ignitech end, the pins are numbered. It's all in the installation instructions that you can download from the Ignitech website (if you didn't get it with the unit).
As far as the tacho is concerned, I suppose the wires will be colour coded. I'd guess it has 4 wires hanging out of it - power, earth, signal input and illumination. I'd suggest you get hold of a wiring diagram for the donor bike.
Tippie said:
Cam, do you know if the signal from pin 15 can be tested with ac voltmeter?
Yes. You can use either the AC or DC voltmeter scales (DC will work because the voltage doesn't go negative). The output either 12V or 0. With the engine running, the meter should read the RMS value of 6V. With the engine stopped, it'll be either 0 or 12V depending where in the phase cycle it stops.
The above info came to me in an email exchange with Ignitech after I was trying to diagnose a non-functioning tacho on a mate's Guzzi after I'd installed an Ignitech on it for him. It turned out that there was a fault in the Ignitech unit and there was no signal on pin 15. They offered to fix or replace the unit, but they wanted it sent back to their factory for testing first. He didn't want the bike off the road for the postage turn-around time to the Czech Republic and back, so declined the offer. I ended up using the coil negative terminal as the tacho input. It's basically the same signal, 0 - 12V and had coincidentally the correct pulse rate of 1 per rev that the tacho needed (wasted spark type ignition setup). If your Ignitech unit is also malfunctioning, you may be able to do the same, provided the coil pulses are the right frequency for your tacho.
If you're still getting spurious tacho readings, then I'd guess it's interference from somewhere. The filter may be the answer.