misterious wires

[LCAM-01XA]

Hey y'all, still trying to sort out the hacks someone who owned my truck before me did. I have this rubber grommet on the driver-side floorboard near the e-brake cable entry, there are three wires coming through it - one blue and two red ones. The blue and one of the red ones have been spliced to something, which was later removed, so they're just sitting there now. The other red wire has been spliced to a black wire leading up to the BOO switch on the brake pedal, however that black wire has been spliced to the BOO switch too, and really don't look like it belongs there. Here are pics of what I'm talking about:

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That short and thin piece of red wire at the BOO switch is a remainder from the splice, it comes off that blue union.

Additionally under the carpet right below the pedals there is a very long black wire that is just loose there, it disappears towards the tranny hump and back. Now, this truck has running board lights that have at some point been de-wired, so I suppose that undercarpet wire is the main power feed for them, but what about the others? Those two loose wires and the BOO splice kinda scare me, does anyone know what they are supposed to be for? All my lights are working, well maybe with two exceptions - my map lights over the seat, and maybe the the backup lights (not sure about the backups tho, can't see them) - everything else seems fine... Suggestions?

 

[TLBREWER]

My guess would be a trailer brake controller was installed at one time.

Tom

 

[sle2115]

My guess would be a trailer brake controller was installed at one time.

Tom

Yep, exactly what I was going to post!

 

[rubberfish]

Me three.
The blue wire is a give away.

 

[LCAM-01XA]

Truck does indeed have a 7-pin trailer connector, but I guess now it won't work the brakes of a trailer cause no controller, right? You think I can hook up a controller to these wires and it will work?

 

[sle2115]

Truck does indeed have a 7-pin trailer connector, but I guess now it won't work the brakes of a trailer cause no controller, right? You think I can hook up a controller to these wires and it will work?

I would guess so, but a quick check from the firewall/engine side should allow you to track them. I wouldn't just assume, but I am sure that was probably what they were for.

 

[icanfixall]

That is for trailer brakes.... Those are great pictures. Be proud of them. Some pics here are really blurry.

 

[LCAM-01XA]

I would guess so, but a quick check from the firewall/engine side should allow you to track them. I wouldn't just assume, but I am sure that was probably what they were for.

Actually I tried that and I lost them - I can feel where they come out of the firewall, a few inches away I can actually see the harness, but then it disappears under other harnesses and plugs and stuff - you know the mess between the master cylinder and the fender, somewhere there under the cruise control actuator is where I lose them.

That is for trailer brakes.... Those are great pictures. Be proud of them. Some pics here are really blurry.

Thanks, I have a decent camera and I always let it do its thing before taking a shot. I know what you mean tho, seen plenty of them blurry pics myself

 

[LCAM-01XA]

Also, upon further inspection today:
- the three wires coming off the grommet are blue, red with a green tracer, and solid red which is also fatter than the other two.
- the long black wire under the carper goes through the grommet for the speedometer, and may very well be ground to battery like someone suggested, especially since I just found a black wire with a ring terminal on it hanging loose behind the passenger-side battery.
- the short black wire was spliced from the fat red wire off the grommet to a fairly thick yellow wire coming off the BOO switch on the pedal, this yellow wire connects to nothing else
- the two green wires off the BOO switch are intact.

My suspicion of wiring use:
- yellow BOO switch wire -> triggers the missing brake controller.
- long black undercrapet wire -> ground for missing controller
- fat red grommet wire -> main power for the missing controller.
- blue grommet wire wire -> connects controller to trailer brakes
- red grommet wire with green tracer -> unknown

Does that make sense? Any ideas what the red wire with green tracer does? The whole grommet thing looks like a factory job, as on the engine side of the firewall the harness is tucked so well no aftermarket installer can even get to it without removing a whole bunch of stuff, and backyard hack-job "mechanics" rarely go though so much trouble for running just some wires. Also, a bit more general question - how will the brake controller know how hard I'm pressing the brakes, is there something in the BOO switch that can feel pedal effort and vary voltage accordingly so the brake controller picks it up from there?

 

[Mr_Roboto]

Most likely the truck had a factory tow package which would have come with that wiring run to the back plug.

Electric brake controllers either use a pendulum to sense braking, or use a "timed" apply which basically applies the brakes harder the longer you have them applied. The BOO is a simple on/off switch.

Some of the older ones plumbed into the brake system itself to sense pressure, not sure if these are sold anymore as I don't believe they play well with ABS.

 

[LCAM-01XA]

Okay, so according to that site here (http://67.18.170.154/home/wiring.asp) the red wire with green tracer should be for the brake lights - however I just disconnected that splice and brake lights still work! So whatever that red/green brakes wire is, it is not needed to run the truck's brake lights...

Also I looked at the wiring manual for the Tekonsha controller for some ideas, they say for '89-'91 Ford trucks and vans with ABS to not use the BOO switch as a trigger for the controller, but to wire it to some green wire at the turn signal harness... and now I'm lost completely, lol - would it make sense if the stock controller takes its trigger from the truck's brake lights? Like, that red/green wire is just a feedback from the brake lights so when they energize they engage the controller too? If that's the case, then what the heck is that yellow wire from the BOO switch for? Tis fairly heavy gauge, like 14 or so, unlike the two green wires that are like 18awg or so..

 

[7.3shrk]

It sounds like you are trying to sort out the previous mess. If it worked well, it would probably still be there. If you are going to hook up a new controller, you might consider just starting over. Who knows if the wire was rigged down stream in the mess.

 

[LCAM-01XA]

Shark, my problem is that both the red/green wire from that plug, and the yellow wire off the BOO switch are factory stuff, not hacked in by some previous owner. I'm just trying to figure out what they're there for, pretty sure one is the trigger for the stock controller, but which is which, and what's the other one for, beats me...

 

[JPR]

On my 91 the three wires from the firewall terminated in a gray connector for the trailer brake controller.

 

[LCAM-01XA]

JPR, that would make sense - power in through the solid red, trigger through the red/green, power out through the blue one, and controller grounds likely through its mount to the dashboard's metal bracing. Would you happen to remember a yellow wire coming out form the BOO switch too?