Project Doris - Imp Gauges Demystified Part 1 - 204846

Progress on Project Doris has almost stalled but I decided to pull a few of the planned features forward as I have seen more than one query on adding standard imp gauges back to the cars. These seem to be met with confusion but the bottom line is you need the right sender (NOT A SWITCH) and first understand how they work. Diagnosing which end is at fault is not complex, it is a single wire circuit almost end to end.
So, you have removed the black top "sender" which is most likely a switch and fitted a sender, Part number TT4802/O0A as per Tim Morgans post but most importantly your sender MUST have a negative coefficient and in plain speak that means its internal resistance drops as temperature rises and more current means more gauge movement.
If you just want to test your gauge, Part 2 is what you are after :-)