Phase 2 Coolant Level Sensor Wires And Testing

[Henry Yorke 269 3 Cars]

Three questions here:

There are 3 wires which go to the coolant level sensor on a phase 2 black expansion tank

Green: Earth

Yellow: 12V Feed to the dash light for the warning when earthed

Red: ????? but has 12V

 

Secondly:

How can you bench test a coolant level sensor off the car as I am sure mine did work but when I connect it up to the loom when it is out of the car (i.e. not in water) then it does not put the light on. The probe tips look shiny and the whole thing doesn't seem in too bad a condition.

 

Thirdly:

Has anyone tried to fit a sender from another model with success? I know the length of the contacts can be different for different level warnings.