I've had issues with the tail lights since I got this truck 3 months ago. First, someone had cut the wiring off just after the wiring harness, I installed new wiring. With the new wiring, at first the brake lights and turn signals would work, but no brake/signal/tail lights at all with the headlights on. Only about half of the instrument panel lights worked, hitting the dimmer switch to "bright", they would all come on. Then the brake lights stopped working.

I've replaced the dimmer switch, headlight switch, brake light switch on the master cylinder, and installed new fuses. I found that one of the instrument panel bulb sockets was not snapped into place, I put that in correctly and magically my dome light worked, all the instrument panel lights worked correctly, and I had tail lights when the headlights are on! Still no brake lights, and no turn signals when the headlights are on.

In the last week I have been able to narrow down that when the headlights are on, both filaments in the bulbs are on. I was investigating this today, I took off the lens covers to get a better look and found out the following:

1. If I remove the screws attaching the sockets to the bed, and allow the sockets to hang down by the wires, neither one works if I turn on the turn signals, or turn on the headlights.

2. If I mount 1 socket to the body, turn on headlights, both filaments light up on that side. The socket not screwed into the bed (hanging by the wires) will actually work properly. I turn on the headlights, 1 filament lights up, and turning on the turn signal causes it to blink. Works same on either side, whichever socket is mounted has both filaments light up with the headlights on, and the other side will work properly. But installing both or letting both hang, they don't work. As soon as the properly working socket comes into contact with the bed, both filaments light up.

I assume this is some sort of grounding issue, but I have no idea what to do. I feel closer than ever to figuring this out, but at the same time...I'm finally out of ideas.

Any guidance would be most appreciated.

 

Do you have a wiring diagram for your truck? If not, it's a valuable tool to have. They only cost about $7 from several vendors, and can even be found for free in some cases here on the forum. Some jerk has done you a terrible disservice by cutting up your harness - however that's what you're stuck with. Maybe you can salvage what you have with the help of a diagram and the color codes. Worst case scenario, you may have to start over with new (and unfortunately pricey) wiring. Except for the financial pain, new modern wires and fuses and more circuits can only be a good thing. Good luck!

 

Brake lights only work if key is "on."

1964/66 F100/250 2WD & 1966 F100 4WD Styleside tail lamps are the same as 1966 Bronco. 1967/72 F100/350 Stylesides & 1967/77 Bronco similar, but have back up lamps.

 

Ck your ground connections the right frame rail is the best place for grounds
That is we're your neg battery connection is clean all grounds
Then start with mult meter one circuit at a time for continuity
Use no-ox grease at connections
Be careful when pulling elect plugs apart they are corroded and will break easily
You will need a shop manual at the very least
Remember rust is not a good contact
Good luck

 

I have a shop manual that has a wiring diagram in it. I did look into new wiring, and yeah it's pretty much beyond my budget right now.

I wonder if I didn't run the brown wire correctly. I ran the green and yellow ones from the firewall directly to each side socket, the brown one I ran back to the last frame cross member and made a simple splice to run a brown wire to each side. In the diagram that NumberDummy posted, I noticed something that I circled in red. I'm not sure what that is? I didn't do anything like that.

 

Thank you for the diagram! I have seen the topic on here before about the brake lights only working when the key is on, and some people saying they work on their truck with the key off. The brief 2 weeks or so that mine worked, they worked with the key off. But mine has some really great custom wiring going on. In addition to the wiring being cut off at the harness, they had a wire going from the horn to the stop light switch on the master cylinder for some reason, among other revolutionary wiring ideas.

I forgot to mention that my truck is a wrong bed, but I assume the wiring would still be the same, that the only difference would be the style of tail lights shown in the diagram?

 

Thank you, I'm going to give it another try in the next couple days.

 

1961/66 "wrong" bed, rear bumper was optional.

 

Hi Bill-

Thanks for that, I don't know if this will solve the problem but it gives me something to try. In that diagram, it shows part numbers 13217 and 13211, they appear to be gaskets and there is nothing like that on my truck. On mine, the sockets are attached directly to the bed with nothing in between. I wonder if those 13217 gaskets would correct this? I'm gonna try to make a couple later today and see what happens.

 

13211 gasket keeps water from entering socket, 13217 is basically just a mounting pad.

 

[quote=SocialDistortionFan;13320724]

If I mount 1 socket to the body, turn on headlights, both filaments light up on that side. The socket not screwed into the bed (hanging by the wires) will actually work properly. I turn on the headlights, 1 filament lights up, and turning on the turn signal causes it to blink. Works same on either side, whichever socket is mounted has both filaments light up with the headlights on, and the other side will work properly. But installing both or letting both hang, they don't work. As soon as the properly working socket comes into contact with the bed, both filaments light up.
quote]

Are you sure???????????

LOL

Been there, went crazy.

I am sorry but this is a typical electrical problem with these old trucks. Clean all your grounds, use a dremel tool or sand paper to make the area and connector shine, add grounds as needed. Frame to bed, frame to cab, frame to engine, engine to cab, battery to frame, instrument panel to cab, grill to frame. You will be surprised how much better everything works.

Electrons take the path of least resistance and a bad ground sends them to strange places as they find their way back to the battery.

After grounds are installed and cleaned, verify your light sockets are well grounded to the holder and to the bed or grill. You can cheat by using a small screw to get a good ground between a socket and he holder.

Verify no wires are grounded or pinched together, verify the wires have good continuity from end to end. Good luck.

 

2nd the idea with going over all the wiring harness plugs and SAE electrical connectors. At the fire wall, those all spewed this green and white corrosion, powder when disconnected. Tried "contact cleaner" that helps for a little while, but NO-OX-ID is the stuff for electrical connectors. They have stayed clean and corrosion free. Great for bulb bases, ground connections, fuse and relay connections, anywhere corrosion is a problem.

Brake lights should light up even w/o ignition ON. Sorry to hear about the wiring woes. Electrical problems can be very difficult to fix, even if somebody hasn't hacked everything all up.

 

One a the mysteries of the ages, they should light up, but they don't. Owned a 1965 F100 from 3/1965 thru 11/2009, key had to be on for brake (stop) lights to work.

 

[quote=old broke prospector;13322457]Thank you! I replaced some ground wires that were badly corroded and insulation cracking off, 1 was from the firewall to transmission, the other was from starter to frame. They were 4 gauge battery type cables, is that the correct wire to use when I do the rest of the grounds you mention?

 

I will try this also, thank you!