Mystery wire?

[MeToo]

This might be a silly question but my '76 Fleetwood has a black wire plugged into the passenger's side cylinder head area just behind the generator, the wire then goes into a plastic conduit (installed by previous owner). This conduit runs all the way to the back of the engine with a T junction that goes to the carb. I noticed today this wire was disconnected.

What is this wire? What is it for?
I know its not the engine metal temp switch as the manual says thats on the back of the driver's side head. I can't work it out from the manual either. Any ideas?
Thanks

[Gene Beaird]

A picture would be handy.

[Scot Minesinger]

This wire connected behind the generator on pass side is the "make sure engine is warmed up before allowing heat to run when it is cold outside" switch.  It is a bi-metallic thermal switch that activates around 140'F and makes ground.  If this is disconnected, thereby making ground an impossibility, then your car heat system may not work unless it is grounded prematurely to this.  If you look on the climate control wiring diagram, this should show up.

If your heat does not work, ground this wire and it may work.

Be careful replacing this switch if you decide to.  Often claims are made for it as a replacement but it is really a block is too hot sensor that trips past 250'F and it will never allow heat to run.

Since most cars are not driven in extreme cold, I usually ground this wire and abandon the delay.  This also cures a problem in the dash switch for a/c which is a frequent problem. 

There are two circuits that keep climate control from operating when the system is not ready to provide comfort.  One is this for heat, and the other is in dash switch for a/c that enables blower fan after a/c is ready to deliver cool air, which is often quick and this switch is the weak link of dash switch.  However when car is warmed up if the sensor behind generator is functional it will allow a/c to work if dash switch is no good.

[cadman56]

Scot is correct on the blower relay till engine warms up.  Larry