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. 

Do you have the OEM ECU that you can test it with?

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.

Thanks for the replies, yes I still have the original ECU and that was my first thought to swap them around to see what happens and then go from there. I’ll go out now and swap them over. Mad Farquhar my bike is a 2005 V11 Coppa Italia, which I think, shares some of the wiring of sorts as the 11 Sport. Which means there are gremlins in there for sure. The bike had some issues when new I believe with relays and poor connections. I brought it in 2007 with 10,000K on it. It now has 35,000k    

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.  :-[ ;D   

Check that the tacho is getting 12 Volts with the ignition ON, the earlier Guzzis picked this up from the headlight relay.
I don't mean the panel lamps, the tacho has a 12 Volt terminal to supply the electronics inside.
Roy