I have a f100 custom long bed I bought from my father in law twenty two years ago and have taken it down to the frame and back up again. Trying to finish installing the air condinditoner ( as it's hot in texoma country) but have ran into electrical problems that seem to have gotten worse. I thought that it was a bad tss so I replaced it as well as head light switch. Think there's a gremlin in the cab of my truck. Haha. I can hit the brake pedal and the brake lights come on as well do all of the running lights. If the lights are on then only one brake light works. With lights off the turn signals work but make dash lights blink. With lights on the turn signals don't work. So it gets stranger. I pulled the steering wheel and was checking the harness of tss and when I put the wheel back on the dome light came on when I push down on the steering wheel. It get stranger cause it's doing this while the tss is disconnected and the neutral safety is also unplugged. But the ignition switch has to be in the run position. I have read many of the forums from this site seeking to find answers from others who know about these old trucks. i went thru the truck and cleaned all ground connections at battery to frame, tail lights, front marker lights, frame to tail light harness, and the one behind instrument cluster. There has been some bad wiring problems from the harness behind instrument panel but was working fine till a few months ago.

 

It is a ground problem, as you suspect, sounds like a ground strap is missing or maybe paint is interfering with the connection somewhere. Battery negative should go to block, another from block to frame. And another from block to firewall.

 

Do you have the main ground cable to the engine, and a secondary ground (10ga wire is typical) to the body?
There should also be a secondary (but extremely important) ground connection between the back of the engine (usually from the intake manifold) to the firewall.

The frame's need for grounding is minimal, but the body's is critical for proper functioning of all the circuits.
Now, I always ground the frame anyway when I'm messing about with wires, but only a few very low load items get their ground from the frame. All the fun stuff happens at the body grounds.

You could have other issues, but an underlying one sure does sound like a grounding issue.

Good luck.

paul

 

I knew it was a good idea to join this site. I do not have a ground to the fire wall from the block or frame. I remember there is no grounding strap at the back of motor. I will install a grounding strap tonight after church and see if this will take care of problems. Thanks for the help, I'll let ya know what happens.

 

Good grounds are critical to any electrical system new or old, in the auto world for quick starts in both cold and hot weather and good battery charging. The automotive environment under the hood is pretty tough on electrics. Road salt and pollution degrades them, eventually they fail altogether, many people are familiar with the battery posts and terminal corrosion preventing engine cranking but the other connections and grounds are just as important.

These older trucks suffer from rust but even new trucks are not immune. Restored trucks might get a fresh thick coat of paint and the result is the same - electrical gremlins. Grind down to bright shiny metal at all connection points and tighten securely. Coat with vaseline or NO-OX to keep the corrosion away.

Those big rubber block connectors that go through the firewall, the pins and receptacles will also corrode, a little time with a brass bristle brush and some WD40 will clean those up.

 

Thanks. Crossing fingers here for sure.

It might not solve all the issues, but at least it'll keep you from fighting grounding issues while trying to track down a pesky and clever gremlin.

Good luck.

Paul

 

Well it sure didn't change anything. But now I have no brake lights. I need a wiring diagram for this ol girl. Is there a place on this site with diagrams? Guess I will have to go thru each circuit. About to park it if I can't get these lights going. How hard would it be to rewire this truck. I have seen complete kits on line for factory connections. It would take care of this gremlin, but also might create another. It already the start of another day and I have got to get some sleep before I turn into a gremlin.

 

This probably won't fix it all, but you want to be sure that your rag-joint provides electrical continuity from the steering column to the steering box. That might get you your horn back if it's not working. A jumper wire with a ring terminal on each end is a common fix.

There is also a body ground behind the instrument cluster which is important.

And if you changed the instrument cluster, you might've gotten one with a different floppy circuit board on it, which will cause some mismatched circuits. The circuit board and the harness which plugs in to it are a matched set.

 

Well I got the lights all working finally and after putting the dash back together I have now got no interior lights. Blew the fuse and no have none working. Always something to do.

 

By interior lights, do you mean the gauge lights, or the dome light? If it's the gauge lights, did you just put in a new stereo? That light blue wire is for the light inside the radio, and will pop the fuse if used as a ground.

 

Dome light is out. The strange thing is it was out one night then the next morning it worked then two min later it was out again and the fuse is blown again. No changes, just put everything back together and it all stopped. I disconnected cig lighter and only the dome remains and it still is out. Gonna check light switch, even though it is a week old.

 

After searching for the electrical gremlin in the truck I finally found it. The wire diagram I got off line traced the negative wire to the body and found three bad connection. Repaired it and secured better and all lights back to normal and got the ac controls to work. Now it's time to charge ac system. Thanks for the help guys.