When I took the bike out for a run on the weekend the Tacho wasn't working, I set switch number 3 in ECU for multifunction display alternatively showing RPM and throttle position when I first installed the ECU and haven’t touched it since. Any test pointers to find the fault would be most appreciated. Hopefully it’s not a dead Tacho. The bike still runs great.

There are some issues with earthing on 1100 Sport inj causing malfuctions on the tachs. It is documented somewhere - could be on Carl Allisons site? Maybe it's something (relatively) that simple - if you have a Sporti. It's a piss poor earth route from the instruments to the battery which corrosion and other dirt can affect IIRC at the fairing / instruments subframe to spine junction. I whacked a couple of extra earth straps on in the early days... but there was some mention of erratic readings manifested before none at all - maybe / maybe not your problem. Just a thought.

KISS, keep it simple stupid. I looked at some of the fuses and then swapped the ECU’s over. No change. I noticed that the head light wasn’t on and having looked at some wiring diagrams when Mad Farquahr had that connection with no home I remembered that the headlight circuit also gave the Tacho power. I checked the fuses again and found that while not wearing my glass’s that I had put an underrated fuse in the light fuse terminal position. 5amp instead of 15amp. Change the fuse and all is as it should be. You can have a laugh, and I can have a sigh of relief as I thought if the Tacho was dead $$$. Thanks again.