Nevada Tacho Not Working Properly

Hi All,

My 750, 2002 Nevada has a strange tacho problem as follows: works fine for 10 mins or so; then the needle drops down to around 500 - 1000 rpm. Give it another 10 mins and the needle drops to 0. This takes longer to happen in the winter than the summer, so I deduce it is something to do with temperature of either the engine or the surrounding air?
I did mention this to a main dealer and was told it would be some 2 hours or so of workshop time to find the fault(s); this would be enough money let alone the cost of supplying and fitting new parts. I am more than happy and able to do the work myself; (and it is a big IF) I new what was wrong in the first place. Can anyone help me please?

my mate had a similar problem and it ended up being the 60 degree drive between the tacho and cable i think they’re about £60+ if you’re anywhere near Scunthorpe you are welcome to visit me and try one of my spares.

Is it electrical or cable driven?