200tdi temperature gauge issue

So here's an interesting one.

200tdi temperature guage won't work unless I pull the wash/wiper fuse, at which point it reads normally.

The wash wiper fuse will periodically fail as well.

I've checked all of the wiring and can find no signs of broken/chafed wires and I've checked all the earths as well.

Wipers/washer pump work normally until fuse fails.

Any suggestions where to focus my attention would be much appreciated.

The gauge has three connections. 1. to 12V lighting circuit (that lights the gauge) 2. 12V from the aux circuit (for power) and 3. a cable that runs directly from the gauge to the sensor at the front of the engine (essentailly the earth).

The same 12v aux circuit powers, amongst other things, the windscreen wipers too (ie they only work when the ignition is on).
I would check to see how the 12V supply is given to the gauge or if it has been 'tapped into' by a previous owner.
It maybe worth replacing this 12V feed with a wire directly from (for example) the 12V feed to the fuel gauge or any other on the aux circuit.