Light problem

[66patrick]

On my '68 D100, I've lost all rear lighting, except the tag light. No brake lights. No blinkers. No running lights. ONLY on the rears! The headlights, front park lights and the front blinkers are fine. Gotta be a ground problem. Any ideas?

[Hobcobble]

Gotta be a ground problem. Any ideas?

Yeah.... Ground problem.
Really though.... check and clean up the grounds. Also, check your
lamp fuses as well as the fuse block clips for them.
John

[66patrick]

Checked all of the connections by unplugging all of the connectors one by one, and reconnecting them. I've also removed the tail light housings, cleaned the mounting holes, and reattached the light assemblies to the bed. The only light that worked all the time was the tag light, and get this! It would light up when I hit the brakes, and it would be the only lamp that lit in the back!

This morning, I used the truck for some hauling and cleaning around my property. All of the rear lights worked! For a while, anyway. Then they quit. Then they decided to work again. WTF, over?

[712edf]

I know its a different animal but when my 75 starts acting up the first place I check is the fuse box. Sometimes I have to pop a fuse out & rub it w sandpaper to get a good connection.
And I have had gauges (oil/temp/fuel) appear to be dead because the ignition switch wasn't making proper contact, even thought motor would be running. A jiggle of the key would bring the gauges to life.

Since yours seemingly work intermittently then yes its a ground or continuity issue & not likely a broken/failed component.

Bucky

[pwadventurer]

Did you check the equipment ground jumper wire between the cab and bed located on drivers side? The tag light might only work because its connected to the frame and bumper. You might also check for power at the firewall connector for the brake, tail and turn signal, if the jumper wire checks out.

[66patrick]

This truck had a four-pin round trailer connector on it when I bought it. I cut the wires from it off a few weeks back. Well, it turns out that there was a spot where two cut wires were touching each other at the cut, so that is what was causing the intermittent lights.

[WD]

Good find, when mine did that it was because the turn signal cam plate had snapped, everything was shorting through the column.

[66patrick]

Oops, spoke too soon! I went to drive the truck last night, and no taillights, brake lights, b/u lamps or t/signals again! I've had every single lamp connection apart, cleaned the terminals, removed the bulbs, cleaned the sockets and the lamp bases both, and even removed the light assemblies entirely to clean the attachment screws and captive nuts...again...

...Nothing. Except, the tag light works when I hit the brake lights, use the turnsignals, or hit the brakes. That one lamp works, no matter what. WTF?

Next stop is the brake light switch (replaced that a few weeks back), and then the turnsignal switch in the column.

[WD]

I ended up going from Utah to TN with no brake lights at all, had to unplug the brand new switch, they wouldn't turn off.

[Hobcobble]

Oops, spoke too soon! I went to drive the truck last night, and no taillights, brake lights, b/u lamps or t/signals again! I've had every single lamp connection apart, cleaned the terminals, removed the bulbs, cleaned the sockets and the lamp bases both, and even removed the light assemblies entirely to clean the attachment screws and captive nuts...again...

...Nothing. Except, the tag light works when I hit the brake lights, use the turnsignals, or hit the brakes. That one lamp works, no matter what. WTF?

Next stop is the brake light switch (replaced that a few weeks back), and then the turnsignal switch in the column.

I've had three similar occurrences with three different trucks....
One ended up being a worn out turn signal switch.

One ended up being a short in the section of harness going to the
rear lights. Of course, it was at the other end of where I began to
unravel the factory tape wrapping....

One ended up being a cracked fuse clip in the fuse block. It "appeared"
to be fine when just looking at the fuse in that location. As the fuse wasn't
blown, I simply continued my investigation. I then came back after re-testing
that part of the circuit and when I actually pulled the fuse out, half of the
spring clip fell out with it. ....
John

[pwadventurer]

Pull both rear brake lamps out of the socket and see if the tag light still comes on when using the brakes. If the tag light stops working, then put the lamps back in and put a jumper wire between the frame and bed and see if that's solves the problem.

The parking lamp circuit is separate from the bake/ turn circuit, so if the parking lamps don't work too, it's sounds like lack of a good ground.

[66patrick]

Cool, I'll check those things to see if I can get this beast back on the road. I nearly got rear-ended the last time I drove it!

[robertob]

I have had trouble with a buried bundle of bullet connections under the cab on my truck. It is wrapped with the harness going to the lights and you wouldn't know it was there unless you look for it.

[66patrick]

I changed a bulb that looked good with a known good bulb. Damn thing still wasn't working! Walked away for a few minutes, then swapped bulbs side-to-side. Guess what? It decided to work again! For how long now, is the burning question...

[66patrick]

OK, guys, dig this! Now, when I have the headlights or park lights ON, and I activate either the left OR right t/signal, they alternate flashes! Left turn = Left t/s lamp goes like normal, but the right t/s will go on as the left t/s goes off, and about half the brightness! The opposite is true, too.

BUT, if the h/lights or park lights are OFF, the flashers all work normally. Goofy.

[EGroscup]

That is a classic bad ground symptom. The bed is not grounded properly to the rest of the truck. Run a jumper wire from the bed to the frame and make sure that there is a good ground connection between the frame and wherever the battery negative is connected.

[66patrick]

I'm going to run a new ground wire from the bed to the frame tonight. The battery is properly grounded, and there are good battery to engine, engine to frame, and body to battery grounds. I had the lamps working briefly yesterday. I hate electrical problems.

[Oldguy]

There is a special little gremlin that spends entirely too much time messing with wiring on our trucks. One of these days I'm going to catch him and when I do he's not long for this world! Mike

[EGroscup]

Good luck Patrick, I once had a 65 Chev half ton that was so rusty I had to run the ground wire from the taillight housing to the frame. Our trucks can even have a poor connection where the bulb socket is swaged into the lamp housing. Erik

[66patrick]

I ran a very stout ground wire from the base of the left taillight housing to the frame rail. I took a wire wheel to the frame point and the taillight mounting hole to ensure a good ground...

Nothing.

More %@!)%^&&*^%&**$%^%&-ing nothing.

Oh, but that damn tag light works, no matter what!

I've been from the dash to the taillights, looking for anything out of place, frayed, broken, etc. The lights HAVE worked before, so I know for certain the wires are all hooked up right as stock. This is really pissing me off.