Coil on Firewall: What is It?

[colnago]

My truck has a block in the engine compartment, in front of the driver, with three rows of coils that look like springs. One end is connected to the wiring harness, and the other end is not currently connected to anything. What does this do, and any idea of where the blue wire broke off of?

Thanks,

Joseph

[basketcase0302]

Joseph,
The coils your describing sound like resistance wiring of some sort to drop voltage. I believe that blue is the color typically used for electric trailer brakes on our trucks.
A picture would be nice.

[colnago]

Jeff,

Here you go. I'm not sure it tells you anything, but it sure has me stumped. It's not necessary for the truck to run. She was originally a Camper Special, so maybe you have something on the trailer brake theory. When I got the truck, it didn't have any wiring for a trailer, or any rear bumper, so anything is possible. I just figured that when I got a bit further, I'd install an under-the-dash trailer brake controller. Did trucks even have the seven-wire trailer harnesses back in the 60's, or did they only use the six-wire harness back in "the day"?

Thanks,

Joseph

[basketcase0302]

Did trucks even have the seven-wire trailer harnesses back in the 60's, or did they only use the six-wire harness back in "the day"?

Sure hope someone else pipes in here Joseph. If it's not a 1st generation brake controller, I'm at a loss here. It is resistance wiring of some sort to drop voltage to something, (brakes possibly an electric motor). It's missing wiring to a few of the terminals, (it would have three different voltage outputs-with I believe the bottom left terminal being where a 12 volt supply would hook up). And I don't remember the trucks even having six wires for trailer lights-four was common back then.

[forrestbump]

Joseph, ...and you too Jeff,

One of my 1970 F250 C/S has the exact same electrical contraptions bolted to the D/S inner fender panel. This truck also has a period correct camper shell and Kelsey Hayes brake controller on it...dealer installation maybe?

Since this truck is a period correct, unmolested survivor, I'll try and trace the wiring on this stuff in a few days and see if it's wired to the camper (doubt it) or to the brake controller (more likely.)

I'll report my findings to this thread in a few days...as long as my memory doesn't fail me (OFTEN) in my advanced years...

[1972hiboy]

Just wanted to add, my 72 camper special ranger has this unit on its d/s inner fender too. the truck is a very unmolested original owner truck. Since it is a camper special I had always written it off as something the previous owner had installed for the cabover camper. But the truck does have a time period correct brake controller mounted to the column and a massive tow hitch setup. However the early brake controllers were tied into the trucks hydraulic brake system usually via a "T" fitting coming off the master cylinder. My guess would still be this is something to do with supplying power to a cabover camper.

[basketcase0302]

My guess is still brake related. The coils provide resistance just as a heater coil or lighting filament does to electricity. Are you back yet Larry...

[colnago]

I'm thinking brakes, too. My truck doesn't have any holes in the bed that would run up to a cabover camper.

Joseph

[fmartin_gila1]

CORRECT - The coils are resistance wires to limit the power applied to the trailer brakes depending upon how many axles had brakes installed and how much weight was on the trailer. This was the old-school way prior to the electronic controls.

Fred

[colnago]

Fred,

Any links to any wiring schematics? Dunno if I'll use it, but I'd like to see how it was originally set up.

Thanks,

Joseph

[tidybowl]

I just removed this system from my 70 F-250 camper special. The brake controller(hydro/electric) was attached to the output side of the coils then ran to the 5 wire plug at the rear of the truck. Just like the resister coil for the ignition, it reduced the voltage when you stepped on the brake it supplied power thru the set of coils. The harder you braked and the longer you braked it heated the coils to adjust the power so the trailer brakes didn't just slam on. This is pre-electronic/ non diode-resister variable unit usually installed at the dealer.You won't fine a wire diagram unless someone has the old one that came with the unit. Even if you are doing a period correct restoration, I would take this out of the system (leave it mounted for looks if you want) and install a new electronic style for safety reasons if you're going to tow with it.