What type of sensor do i need to close 12v circuit measuring low resistance liquid (such as resin or glue) ?

This is what i need.

The reservoir is filled with resin and sensor on the left triggers relay behind, deactivating the pump.

I need some way of closing the circuit when level is reached.

None of the float switches that i know of will work because they are too big to fit.

You need to provide more details. You want a sensor that measures resistance and closes a relay at some preset value.

Why not use two wires being fed from a battery and a series resistor. What range of resistance do you want to measure? By the way, I don't think resin or glue are particularly low resistance, but I don't know for sure.

The wires may have to be gold plated to avoid degredation.

The signal from the sensor would drive a compartor, with the output driving a relay.