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My water temp idiot light has never worked and I'd like fix it. Wire to sender is dead, not live and not earthed. I have looked at the FB wiring diagram but can't work out where this wire is supposed to go to from the switch. Its a red motor and temp switch is on pass anger side at back half of head top.

it must get power to the switch to work, i assumed it should be live and the temp switch earths it once it closes at certain temp, which in turn turns on light when the circuit closes. Bulb is fine and switch is new. I have wired up a thermo fan with close/open temp switch and relay, is the light circuit similar or is it a series/parallel circuit of some kind?

Can someone pls explain this circuit for me or draw me a picture?

Thanks Tim, I studied the wiring diagram some more and armed with your explanation think I understand. I'll pull out the gauge and check the +ve supply. On the wiring diagram looks like the other idiot lights are similarly supplied with power (and they work).

Gave up on it! So far, anyway...,
Autometer mech temp gauge ordered with sender to replace idiot light sender/switch.
Is it possible to somehow use both? If so I will persist with trying to get the idiot light working as a gauge is good to have but a bright red glowing light is what gets your attention. BTW, red 202 & using the 1/2 NPT lower thermostat hole for thermo fan switch. Heater plumbing non existant ATM but will install shortly so can't use those outlets on passenger side of thermostat base.