I have a Trailtech Vapor fitted to my car and I have the tacho feed coming via a screened cable that has the insulated core wrapped 5 times around one of the HT leads. It's not the best, but it does work reasonably well. I have just fitted a set of sequential shift lights which needed wiring up to the ECU tacho output so, having wired this up, I thought I would try connecting the Vapor up to the same ECU tacho feed. The shift light worked perfectly but there is nothing on the Vapor tacho at all (even after resetting the unit). I have since connected the Vapor back to the feed from the HT lead and it's back working the same as it did before but why wouldn't it work from the tacho feed from the ECU.
Any suggestions?

Maybee the vapor requires a 12v pull up resistor ( a resistor of about 1 k connected to the 12v supply and tacho output) or a pull down (connected to the tacho output and negative).

Darren

What ecu are you using? I have the same problem with tacho out of my emerald to a vapor. Opted for the ht wrap solution but it's not neat and I'd rather wire it properly

Stock Aprilia. Having taking advice from Trailtech in the UK, it may be an issue with the power from the ecu causing issues with something on the pcb. In other words, not sure and can't think of a solution.
I have also been advised that my HT lead option will be much smoother if I take the power and earth from the dash direct to the battery rather than from a fused permanent live. Also, I am reverting back to the Vapor lead for the HT lead rather than the screened cable and putting the black to its own separate earth point.