Question about Thermal relays
 

What is the thermal relay and what does it do? Any reason for having or not having it?

'thermal relay'....??? what is it? where is it installed...what wires are affixed to it??? relays are normally electrical devices used to control high amperage loads by an input of much less current...... In other words an electrical controlled switch.

There is a thermal relay in the headlight circuit, in the actual switch I think.
This is basicly a self resetting circuit breaker that will trip if too much current is pulled through the circuit. Things too look fo include wires shorted to ground, poor connections, mega high wattage bulbe, extra lights tapped into on the ircuit, and rarely a shorted out headlamp.

There is also a thermo relay in your transmission controlled spark system (if your truck came with it) it will only make your vacum advance work when in third gear and the engine is at operating temp

Hooter, you sure that isn't just a regular relay like the one for the horn?

What about turn signals and hazard lights, would'nt those be thermal relays. You turn them on and the piece of bi-metal is heated causing it to warp, breaking a contact, cooling down straightening out, then making a contact, and on and on. Sounds thermal to me.:confused: