Relay on lights circuit?
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Post Fiend
Joined: Apr 2008
Posts: 5,338
Likes: 3
From: Grants Pass, Oregon
Relay on lights circuit?
I just noticed something this evening on my 72 bodied F250(i dont drive it much at night),when i pulled the light switch out,i heard a rather distinctive click of a relay,from pass. side of underside of dash. i looked later,and found a relay mounted on pass side kick panel,up high tucked out of sight above and in front of vent. Its marked FoMoCo,and Littelfuse,so im assuming its either original or a dealer offered piece,is this relay typical for this truck? I was of the impression that this era truck had its parking/headlights,etc wired directly switch to light,rather than thru relays. the reason im asking,is this truck was assembled from a 72 body,75 chassis,and engine is probably mid 60's pass. car,SO,wiring is rather jury-rigged.
Senior User
Joined: May 2007
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When the relay trips are you loosing any of your lights??
We had the same issue but it was only occurring when I was towing our travel trailer. We ended up letting the truck and trailer sit in the yard with the lights on and after about 7 minutes it would start to trip and when it did, we lost all of the lights.
I learned that our light system is light duty and the trailer was enough to trip the relay you are mentioning. I ended up running a separate circuit for the running lights on the trailer.
If this is occurring with the truck alone, one suggestion I received was to check the wire harness for bad wires/connections and grounds. If there is any accessories attached to the light circuit I would consider moving them to another.
We had the same issue but it was only occurring when I was towing our travel trailer. We ended up letting the truck and trailer sit in the yard with the lights on and after about 7 minutes it would start to trip and when it did, we lost all of the lights.
I learned that our light system is light duty and the trailer was enough to trip the relay you are mentioning. I ended up running a separate circuit for the running lights on the trailer.
If this is occurring with the truck alone, one suggestion I received was to check the wire harness for bad wires/connections and grounds. If there is any accessories attached to the light circuit I would consider moving them to another.
Thread Starter
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Post Fiend
Joined: Apr 2008
Posts: 5,338
Likes: 3
From: Grants Pass, Oregon
It appears to be a relay,not a breaker,and the click is it engaging. it isnt tripping or cutting power,it seems as if its switching power on. Since my truck is a Camper special(body,at least!) maybe this relay was designed to supply power to camper or aux lighting? i will check my other F250 today(it doesnt appear to be a Camper Special),and see if it has this same relay! thanks,Bob
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Post Fiend
Joined: Apr 2008
Posts: 5,338
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From: Grants Pass, Oregon
The other truck isnt a CS,and doesnt have the relay! it must be a relay to power marker or other lights on a camper,so that they would come on with parking and headlites/tail lights.
Post Fiend
Joined: Jul 2004
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From: Northern California
If you look under your truck, bolted to the frame on the drivers side, just about mid way, you will see the Camper harness plug in.
It has wires for the brakes, turn signals, clearance lamps, and a direct battery feed too among others.
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Post Fiend
Joined: Apr 2008
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From: Grants Pass, Oregon
In my case i dont have the camper harness plug in,but its probably directly related to the fact that my 72 body is on a 75 4wd chassis..... if it has wiring for brakes and signals is it also considered a trailer wiring set-up,or do they make it that way just in case you have a camper that has its own brake and signal lights,and that the camper structure would obscure the factory lights?
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Post Fiend
Joined: Jul 2004
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From: Northern California
.
if it has wiring for brakes and signals is it also considered a trailer wiring set-up,or do they make it that way just in case you have a camper that has its own brake and signal lights,and that the camper structure would obscure the factory lights?
The Camper's Harness would go between the cab and bed, and plug in at the plug, I mentioned earlier bolted to the frame.
Trailer Specials had simular wiring, except the trucks factory plug was located toward the rear.
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Post Fiend
Joined: Apr 2008
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From: Grants Pass, Oregon
The truck has more than its fair share of wires to nowhere,plugs that arent plugged in to anything,etc. Amazingly enough,the majority of the electrical system works fine,the truck always starts,there doesn't appear to be any electrical drain when it sits! im just starting to add some circuits to it,ive installed a 6 fuse panel under the dash,its wired to the starter relay with 8 Ga. wire,circuits that will be "constant hot" will just be wired directly,and circuits that i want only to be "ignition on hot" will have relays to switch them on/off. So far ive only added one circuit,a set of halogen work lights on the back bumper on a toggle switch,relay activated with ignition on,to serve as backup lights.
Freshman User
Joined: Jul 1999
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mine used the relay for the roof lights - 70 F350. I think the switch source is a black wire that come back from the relay to the drivers side (about where the head light switch i) and has a 3 hole bulet type connector. If all three are open.. it was never used. Or unplug the relay and see what goes out!!
Steve
Steve
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Post Fiend
Joined: Apr 2008
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From: Grants Pass, Oregon
steveh,interesting that you mention the 3 hole bullet connector,when i was groveling under the dash installing the fuse block,relay,fuse,wiring,etc, this morning i saw a 3 hole bullet type connector,with one hole plugged only. sounds like the same plug,tomorrow i may just go under and check it with a circuit tester, i wouldnt mind having a circuit available that was switched by the lighting switch..... Thanks,Bob