I've had it both disconnected completely and shorted to earth. At the moment it's earthed streight onto the battery. I metered it quite early on in the problems when i first changed the pressure switch, it was sending 3.5v which didn't seem right to me. I also metered it last week but it was giving 0v but it was getting dark and i was freezing my spuds off so can't say how accurate that could be, lol. Will try this tomorrow, see if it helps. On holiday for a week so got plenty of time to faff about with it now.
Just found this on uk-mkivs.net, which might be worth looking at, as you have covered everything else -
Not yet, been away training for work so not had a chance to get into it. My exhaust broke today as well, sounds kinda nice but this is getting annoying now, lol.