The Stovebolt Site Forums The Shop Area The Electrical Bay Tail Light Gremlins

OK...I am now ready to ask for help (or read instructions if anyone has some). A few days ago the right tail light on my 63 fleetside stop working. The turn signal still worked, but no running light. Checked the obvious things (bulb, brohen wires, etc) but no joy. I'd read on this site that sometimes these old trucks have ground problems due to rust and corrosion behind the housing. I took it apart and cleaned all of surfaces neccessary to get a good ground and in the process found some very suspect wiring installed by the PO. I use "installed" as a very loose term. Lots of wires twisted together with electrical tape, etc. I ordered new tail light pigtails for both sides from ChevyDuty and replaced the wiring harness with all soldered connections. Now when I really have a problem. With the headlights off the turn signals work fine...when the headlights are on the right turn signal will blink, but there is some "winking" on the left side as well. The left turn signal doesn't work at all with the headlights on. The re-wire seemed pretty straight forward with only three wires (brown, green and yellow) comming to the back of the truck. A test light told me that the brown wire was running light, the yellow wire was the left turn signal and the green wire was the right turn signal. The new pigtails came with a black wire and an orange wire. I assumed that the black wire should be hooked to the running lights and the orange wire to the turn signals and hooked them up accordingly. I suspect a ground problem, but I can't find it. Any ideas?

It does sound like a ground problem. Odd problems like this are almost always grounding issues.

Do you have a test lamp? See if you can connect a test lamp across the brass base of the bulb and the negative post on the battery. Almost certainly you'll need to string a jumper wire from the battery to the rear of the truck, but you only need it long enough to do some testing.

Connect the test lamp between the bulb base and the battery post, and then have a helper operate the turn signals. If you have ground problem the test lamp will light up when connected to the base of at least one of the bulbs.

If it were me I'd first double check your wiring job just to be sure. Provided I still thought it was correct I'd just assume the grounding was bad, and look for a way to fix it. The wires you've replaced are only the hot side, not the ground side, so verify that a good electrical path exists between the light bases and ground, and that the ground straps between the battery and frame, and frame and body are all in place.

What OldSub said.

Also, something else to check... when you soldered the wires together, did you leave bare wire or did you shrink wrap it or wrap it in electrical tape?

If the bare leads are touching, that would explain the winking in the other tail light when the blinker is on.

I'm not an electrical expert but I see a potential problem. If the stock wiring harness has three wires running to the back of the truck they would be tail - left turn/brake - right turn/brake. The black & orange wires are probably for backup lights. You have already identified the turn signal wires (yellow & green) If you hooked the black & orange into that same turn signal circuit it's quite possible that is where your gremlin is. The yellow & green aren't just your turn signal they are also the brake wires, both being activated when you apply the brakes. I'd try disconnecting the black & orange wires and see if the gremlin goes away.

Perform the same ground clean-up proceedure on the left tail light that was done on the right. Sometimes the fenders are insulated from the body and a groud wire must be run to the light fixtures from the frame.

Also replace the bulbs with clean new ones, sometimes they short together internally.

on my 61 i had to take the tail light buckets out and sand them shiney, put in new grounding clips, get new mounting screws, and clean up the sheetmetal at the grounding points. I figured this out after doing alot of other work the turned out to be uneccesary but i sorted out some other gremlins in the process, so it was a mixed blessing. i would carefully clean and sand those parts and get new clips at least. they were like $1.50 for 12 and i only needed 4 i think. try that approach it is cheap and easy. it is almost certainly a grounding issue.

Thanks for the ideas. Some of them I've already tried (like rebuilding the loom twice to make sure all connections and insulation were good), but I like the idea of hooking up a lead from the test light to the battery to check for a ground...that seems like a for sure way to find out if I'm chasing a bad ground. Maybe I'll get to try some of these ideas out this evening.

Thanks for posting this. I'm having similar problems with my '70 stepside right now. Good info on places to start!

Texmo, if you get a chance we would like to see you at the Decatur meet on Friday, Feb,24th,(posted in the events section) should be about 12 of us in the DFW, etc get together, most of us will be driving our trucks,, would love to see ya there,, sorry, cant help you on the electrical grimlin,, looks like you have had some good tips.regards....Fred

Joker, I'd love to go to Decatur and hook up with you guys, but I'll be holed up at a seminar for work Feb 22 - 25. I've tried to get out of it multiple times for various reasons, but my boss ain't goin' for it. If you guys get together some other time let me know...I drive my truck every day and would be thrilled to road trip it to share a cup of cup of coffee with you guys. I may give it one more shot at getting out of the seminar...think a swap meet is a good reason??

just do it, that's what I tell my boss, I am taking off,, we usually meet several times a yr, texas motor speedway,, one in arlington, one in grand-parrie,one in Ft. worth... Fred

Here is the latest on the gremlins...

I have tail lights, brake lights and turn signals (mostly). I still get a little "winkage" on the side that is not supposed to be blinking, but I'll live with it for now. I've sanded everything I can reach back to bare metal to ensure a good ground. I've replaced screws and clips with brand new ones. I've re-built the loom three times. The last time I re-built it I checked for correct current flow with a volt meter after every connection. All connections are soldered and heat shrink insulated. My next option for getting a better ground is start removing body panels to try to improve their connection to the frame or solder a ground wire directly to the tail light housing and connect it to the frame. I've tried all of the tricks previously posted...no joy.

I know this is going to turn out to be something stupid...

I dug this up out of the archives to update on what I found in the process of installing my new wiring harness...

I chased fuses, hot wire connections, ground connections, pigtail connections, (including new pigtails, screws, and housings) for several days to no avail. I also sanded every potential ground point I could think of back to bare metal. When I finally decided to re-wire the truck I discovered two wires at the steering column where the PO had stripped the insulation to hook up some accessory, twisted the wires together and wrapped them with electrical tape...the tape had more or less dissolved and the two wires were rubbing together. One had nearly burned in two! The insulation was melted all the way back to the connector...a few more miles and I would have had a melt down!

The moral to this story is that if you start having electrical problems that you can't positively identify its best to start from scratch to make sure that all the hard work you put into making your 'bolt road worthy doesn't go up in smoke.

I have similar problems on my 63 GMC fleetside.

With parking lights off; left turn signal OK, right one works but I get leakage to left tail light and licence plate lamp, both of which flash on about half power.

With parking lights on; left turn signal OK, right one will not work at all. However, I do get power to right rear turn signal which stays constantly on, the lamp is bright too. This is the case even without turn signals on.

Now the fun REALLY begins; we switch the stop lights on!

Stop lights only; left one works OK, no power to right stop light.

Switch left turn signal on, right stop light works but so does the licence plate lamp!

Right turn signal on, left stop lamp OK, licence plate lamp lights without flashing.

When I then switch the parking lamps on, it behaves as above; right turn will not work at all.

HELLLPPPP!!! PLEEASE!! One Limey going crazy over here! :mad: :confused: :mad: :confused:

Kev,
As stated above...I did the same routine that it sounds like you are doing. I chased everything I could think of to no avail. The good part is that when I finish up with the rear end wiring this week I will have all good ground connections to work with as they are all clean, bright and shiny!

The melted wires I found were making contact with each other under the dash which I suspect is what was causing my "bleed over".

If it looks like the PO has been under your dash making questionable connections I would either remove your current harness and repair it properly (i.e. cut, crimp, solder and heat shrink insulation) or replace the whole thing. I chose to replace it since the repair job would have taken just as much time and I still would have ended up with a 40+ year old wiring harness.

By the way, if you haven't been working on the wiring harness lately and everything was working before then it definitely sounds like you have a wire crossed somewhere due to age, corosion or failed insulation. When looking at the dual filament bulbs in the rear the "dim" filament should be your tail lights, and the "bright" filament should be the turn signal. Your description above leads me to believe that somehow you are getting voltage from the running light circuit into the turn signal circuit, hence the "bright" tial light that stays on all the time with the park lamps on.

Update. GOT the S-O-B!!

Inside the rear lamp housing, there was corrosion between the brass insert and the housing itself. Removed the insert (you need to be careful doing this to avoid damaging it) cleaned the rust out, re-assembled it, sorted!

Except ..........

I still only have one stop lamp, driver's side. When left turn signal is on, though, right stop lamp lights up OK, without feeding through to the licence plate lamp or others. Ignition does not have to be on for this to happen.

Any ideas on this one? :confused:

The only thing I could suggest would be the old stand by...ground connection.

I finished up the tail end wiring on my truck yesterday and my right side is dim which leads me to believe I STILL have a weak ground somewhere on the right side. The only thing I haven't checked is where the body panle connects to the frame...that's next.

Thanks, Texmo. I'd guessed that this might still be the problem, but never having worked on one of these before (it's my first "Yank" truck although I've had Harleys for years) I wondered if it might be a quirk in the switch or suchlike.

Strange thing, though, is that it was the right-hand side which I fixed to sort out the other problem. I'll try doing the same for the left side, see if that helps.

Texmo I went through the same thing on a 65 gmc, my electrical freind said ground ground ground.He was right,I think your correct on the theory of sheet metal connection to frame.Think about it the batt is grounded to,the engine or frame and usually the rad support or some type of body ground,but thats all on the cab which is not connected to the box.So the rear ground is relying on its connection with the box to the frame,and after 43 years of use not to mention a wooden floor, ya get the picture,I ran a wire from the housing to the frame and havent had a problem in six years sounds like that was your next step anyway!good luck

Bent,
It is my next step (if I can keep my paying job from getting in the way), but it's nice to know that someone else has gone through the same thing. On some of the 40+ year old dash light bulb housings I soldered a ground wire to the housing and it seems to work. I had considered doing this to the tail lights to eliminate the possibility of bad connections in the body panels. Is this what you did?

YES