I have a wiring problem. Does anyone have a diagram? The person who had the truck before me put in a rear window brake light??? Don't know why? Back brake lights did not work I guess thats why they did it. They also wired it for a camper too so I have a big mess at the back-end of the truck. Well low and behold the light they installed stayed on all the time. I'm sure it is a simple problem but i'm not and expert on wiring.
Thanks!!!!

 

Dont have a diagram for you, but the back of the truck is the easiest.

There should be 4 wires going to the rear of truck(from under cab). 1: reverse lights
2: running lights
3: left turn
4: right turn

Now with that said the running lights is USUALLY a brown wire, the turn signals are yellow and green(I forget which is which for left and right) and dont know the reverse color. A simple test light will confirm what is what.

The rear window brake light was probably NOT wired in correctly for a "single tail light" application, that is why it stayed on. OR maybe they hooked it to the wrong side of the brake switch under the dash and that is why it was always on. Trace the wire from it and remove it so it does NOT create other problems.

It's easiest to get it all back to plain and stock so nothing is creating problems.

Does the truck still have the original wires out back or is it all cut up?? My one truck was all butchered and owner said "leave it alone, it all works". Well I got under there, ran new wires from up front and soldered all connections. It was all good from then on.

Good Luck
Larry

 

Ok everyone i came with this problem yesterday about my light problem on my 1967 P.U. F100. Here is what it is doing and may I say I was under it yesterday I noticed it must of been rewired because I seen the old wiring still there.
First does anyone know how many wires are suppose to be on the brake switch and do they all go to just the 12+ side?
OK here is what is going on:
1.ignation switch is off!! Right turn signal is in the right turn signal position(should not be any power going there because ignation switch is off) BUT!! the left brake light comes on.
2.Put turn signal in the center position,both brake lights on?(should not be because ignation switch off)
3.Put left signal on the position of left turn,right brake light on?
4. Then i go back to center position and then only the right brake is on not both this time?
WITH ignation switch on.
1.put right signal on the turn signal works and the left brake light is on and also slightley blinking.
2.in center position both brake lights are on.
3.put left signal on and that works fine?????BUT with engine running the right brake light stays on???
4.with engine running the turn signal in the center position,right brake light is on?
5.put signal in right position engine running,signal works but again left brake light is on and blinking a little.
When i turn on the head lights all lights are blinking including headlights and park lights????
Man this thing is driving me crazy!!!! Does anyone know what is going on?????
Thanks
Wayne

 

Ok here is my opinion for what it is worth
The brake light switch is stuck closed, the brakelights will work with just the battery....ignition switch off. The turn signal switch interupts the power to the brake light....right turn signal on no power to the right brakelight.
The flashing and other werid stuff is probably due to a bad ground at the light sockets, or maybe a corroded bulb socket.

ps
As far as I can remember there is only 2 wires to the brakelight switch, one on each side of the switch....doesnt matter which side as long as they are on opposite sides. With cruise control I think there may be a few more wires but I have never had cruise control

 

WOW!!

You have a mess on yer hands. Sparky's right about the brake switch. Should only be 2 wires on it. With the brake pedal out you should have 12VDC on only one wire. When brake pedal is in you should have 12VDC on both wires.

If indeed your brake switch is shorted and affecting all your other lights, disconnect one of it's wires and see if it affects your other problems.

Good luck,

 

Has the wiring been messed with?It sounds like you have a real mess.I just went through all of this with my 69 the guy who owned it before me had the signal switch burn out on him.Rather than getting a new one he just cobble nobbled it all back together by jumping wires together WHAT A MESS!!!!My advise to you is if you can't figure it out call a automotive eletrician and for 2 or 3 hundres bucks you will be back on the road in no time at all.

 

If you think its on the tail, then remove at connecter a frame rail then remove and test and fix where the trailer wiring was. then go up forward by the master cylinder there is another plug and test from , I have work on truck that people wire brakes into Radio , cig lighters and have run there own wire, if it does not look natural in there remove It not to bad to fix
GWB

 

Very nice!

Don't you just love people who don't take the time to do a wiring job properly.

I'd also take a look at your hazard light circuit. It should be hot irregardless of ignition switch position, so this may be partially to blame.

 

If you do not have a good testlight and a Volt-ohm meter (preferably digital) then get them. You can't trouble shoot electrical with out them.
The problem isn't as complicated as it seems but trouble shooting these things requires being there which only you are.
I have seen some strange and confusing things due to bad grounds. The electricity trys to find a path back to ground where ever it can and manytimes the only path is through the other element in a dual element bulb, this is called feedback. I have also seen the element in a bulb break and lay across the other post which seemed like an extremely confusing thing to diagnos the symtoms of. Don't over complicate it just yet. Check all the grounds and clean the sockets.
The other advice here is good, start checking at the connectors ect. But first go under the rear of the pickup and look for signs of old repairs or trailer connectors. If you see a big mess like gobs of tape or scotch locs or household wiring twist-on connectors the you really need to straighten that mess up. Also those old wires get brittle under there and break. Another thing that happens is when the steering columns get changed there are two different configurations on the connector for the turn signals and you have to straighten that out. I don't remember which wires you have to switch but it has been covered in other threads recently. Does the pickup have any aftermarket, or owner installed things like radio/stereo or instrument cluster? If the answer is yes, you may now panic. If it is too big a mess you may want to get another harness from a donor vehicle. A savvy mechanic can also straighten it out pretty fast, but remember that only about 10-20% of mechanics really understand electricity any better than you. It may take them forever and they will start lying and yanking your chain to cover the fact that they are clueless. I have had trucks come in on a slideback form other shops that had new alternator, regulator, battery and starter and still weren't fixed. I had a Dodge come in like that once. The other shop had it for 2 weeks and even had the huevos to charge the poor hapless owner full price on parts and labor and then have him tow it away. It took me all of ten minutes to find the problem(fried fusable link). Well now you have some direction and a lot of good advice. Once again check all the grounds including a good body to frame or engine ground, remember the body sets on rubber. I have seen fried speedo cables before because that was the only ground and couldn't carry the load of the starter. Tally HO!!

 

man i got a world of problems too! i have a 68 f100 with some 67 parts that has so many bad wires i have no clue were to start but here it goes. i have no insterment lights but the bulb is good cause i checked that with a hot wire right off the batery then i have two break light setups (one under the dash the other running off the back break line and then i have no cargo lamp but i have not looked at that closly yet pluse i got a bad motor that is at the machine shop for block cleaning, new crank, and new cam bearings! does any one know where i can get a wiring diagram for a 68 pickup under tha dash at least? i am almost ready to say forgt it and get a new rig man.

thanks,
Christopher King

 

It hard to believe But ford did a great thing in these trucks, everything unplugs just before it exit the inside the cab. I think the hardest part is getting the fuse box unscrewd and the wiring to tank and dome light. Then pull the inside and fix, I did a good one myself yesterday, Aftear installing front in and motor, Took truck for test drive and driving truck I thought truck had king pin going bad. Some how the wiring harness manage to get wrap around the rag joint. Its a wonder it did not pull the tail lights loose lol Anyway I think your going to real happy when you get it work out GWB

 

Christopher, these old trucks are plentiful and cheap in Wa. and Or. it seems. Maybe you should just find an unmolested donor and get a new harness. It really isn't that hard to change. Just make sure it is from the same model with the same dash( idiot lights versus full guages.

 

thanks much ill try to do that but with low income tec. it may take some time to find a donor

 

Please update the original thread rather than starting another thread regarding the same topic.

It saves users some searching all over the place, trying to find the follow-up info.

 

I think I have an unmolested harness from the engine compartment back from a 73 if you are interested. I would take out the rear lights and make sure the connection there is okay. I think there is also a connection next to the gas tank? This splits to the two lights from the intial 4 wires running to the back. I'm not sure but I don't think I have this part? From the gas tank back to the lights that is. Let me know.

Funny what people will do. I had a rusted out fuse box so the prior owner rewired the whole truck instead of just replacing the box?

Ken
68 F100 390
74 Bronco 351W