Fuel sender unit

[adyRE]

So I had irregular fuel readings for a while and couldn't trust my gauge so I thought right, I'm going to see what's going on so I removed the fuel sender unit and began testing. I believe these units are ranger around 30-300 Ohms. When I began testing the unit at empty read about 300Ohms but went Open circuit just as I began to move the arm so I thought right it's definitely the sender. Upon closer inspection I found a crack along the carbon resistance board and with my big fingers and a bit of prodding the board fell apart. So now I have a completely knackered fuel sender. Ive attempted to source a replacement to which I'm having no luck at all. Ive bought a fuel sender unit for the same van as mine but its for a diesel van. My existing sender is a 2 wire resistance sensor and the diesel one is a 3 wire. I've tried to wire in the new sensor just using the 2 wires as the resistance range is the same and working. But... It won't read back on the gauge... Do I need to do something with this 3rd wire?? Possibly ground it somewhere for the sender to work. Anyways I'm sure I've got more questions but thos essay is enough for now. Thanks

[Huskyxantia]

Sounds like it needs to be earthed , maybe someone could pop up a wiring diagram for you .