Question about Thermal relays - The 1947 - Present Chevrolet & GMC Truck Message Board Network

zyggy72 · 01-27-2004, 01:39 PM

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

GMC Jim · 01-27-2004, 10:33 PM

'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.

Longhorn Man · 01-28-2004, 12:30 AM

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.

Hooter · 01-28-2004, 03:51 AM

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

Longhorn Man · 01-28-2004, 08:06 AM

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

walker · 01-28-2004, 09:38 AM

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.

01-27-2004, 01:39 PM	#1
zyggy72 Can't kick the addiction! Join Date: Jan 2002 Location: Riverton, CT 06065 Posts: 402	Question about Thermal relays What is the thermal relay and what does it do? Any reason for having or not having it?

01-27-2004, 10:33 PM	#2
GMC Jim Senior Member Join Date: Dec 2002 Location: Portland, Oregon Posts: 901	'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. __________________ '71 GMC;fleetside;PB/PS/AC/CC/402 Eng./Custom Paint/110,000act miles/3 fuel tanks(52gal).

01-28-2004, 03:51 AM	#4
Hooter My other Love Join Date: Aug 2001 Location: Castlegar B.C. Canada Posts: 4,085	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 __________________ Castlegar B.C.The great white North (Canada Eh!) Hooter_5@hotmail.com First generation Monte Carlo club pictures of my life

01-28-2004, 09:38 AM	#6
walker Registered User Join Date: Jul 2003 Location: north of Phx AZ about 30 miles Posts: 698	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. __________________ Andy,Phx AZ '67 C-10 (Ahhh, done at last. Well there is that disk front end I want to put in and...) "23 C-Cab-sold '48 Ford 8N tractor(still working) '67 Scout(Now on the road) '70 MG B.-sold

01-28-2004, 12:30 AM	#3
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,690	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.

01-28-2004, 08:06 AM	#5
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,690	Hooter, you sure that isn't just a regular relay like the one for the horn?



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