Tail light issues

[reeshard08]

I have a 1971 F100 LWB and having issues with my tail lights. The brake lights work maybe 5% of the time, reverse lights are none existent, turn signaIs work sometimes but when the headlights are on, the signal is jumbled. The turn signals work fine in the front. Anyone have any idea how to fix?

[68RGR]

I can't help but think a trailer connector might be involved.

Does your truck have trailer wiring? If so, you would be wise to check it out.

Regardless, there are only 4 wires involved - Left turn/brake, right turn/brake, running lights and backup lights. If I remember correctly, those wires run along the driver's side frame rail. It would be a good idea to find a location between the cab and the rear bumper to identify these wires and verify their functions.

I believe there are a couple of connectors near the rear end of that frame rail that will allow for that. Check the wiring diagram for colors but I believe yellow is left, green is right and brown is for running lights. Backup lights use the black wire with a red stripe.

Based on your description that turning the lights on compounds the problem, it sounds as if the running lights and brake/turn signal lights might be crossed up. A common way for this to happen is when a trailer connector is wired incorrectly. Or, if the trailer wiring or connector are damaged. That could also be the source of the backup light issue but it could also be the switch - Either the neutral safety switch (auto trans) or the switch mounted on the steering column under the hood if you have a manual transmission.

Of course, the wiring could be crossed up at any point between the headlight/brake light/turn signal/backup light switches and the sockets at the rear of the truck. Because the bulbs get their grounds from the shells of the sockets, it would be a good idea to verify that each one has a proper ground. Also check to see that the correct bulbs are installed. Mine uses 1156 for backup and 1157 for brake/turn.

Oddly, just today, I checked the sockets and bulbs on my '68 Ranger and cleaned the inside of the housing and lenses. Thankfully, mine still worked when I was finished!

Good luck and let us know what you find.

[reeshard08]

Thanks 68RGR for the reply. There was a trailer connector "spliced" into the wiring at the tailgate of the vehicle, but I have removed and repaired to "original". The connector that you speak of at the end of the frame I did disconnect and test with a mulitmeter for continutity, and everything checked out there. I also checked the connnections in the taillight bezels as well, and all checked out. Lights are all brand new and proper replacements.

I've read on other posts that maybe this could be a problem with the turn signal switch since the lights all go through that bottleneck. Would this be a possiblity?

[68RGR]

Are you saying the wires in the rear connector functioned properly when you checked them with a meter? If so, the problem should be between that connector and the rear sockets. If not, please clarify what you checked at that connector. It would be a good idea to unplug that connector and check each function (L, R, brake, turn, etc) with a meter or a test light.

I've read the same thing relative to the turn signal switch.

But, that doesn't seem to explain the backup light issue.

I suppose the TS switch could account for some of the problems but you wrote that the front signals work properly. Now, the rear TS/brake lights use the same filaments. So, that might mean the TS switch could be the root of the problem with those functions.

One other thing - Have you checked the emergency flasher switch and its connections? One poster said a P/O had removed the switch and connector and twisted the wires together in his truck! Really SHORT-sighted.

On the backup lights - Manual or auto trans?

[reeshard08]

Okay, so I disconnected the harness from under the hood all the way back to the tail lights. I checked the continuity with a multimeter from the plug under the hood to the tail light bezel. Right turn signal works, left turn signal works, brakes work, and the reverse lights work. So I have narrowed it down to somewhere between the plug under the hood to the dash. I guess the next step is to remove the instrument cluster and check the wires and connections. Because the reverse lights are non-existent, that may be the switch to the transmission, the others not sure yet. Any suggestions on what to check first?

[68RGR]

OK, now you have really narrowed it down. Seems to me it has to be the TS switch or the flasher switch if the under dash wiring is OK. Unless there has been a fire or grossly overheated wiring, you can probably assume the wiring is OK.

What happens when you turn on the emergency flashers? I'm guessing the front lights flash but the rear lights do not or have issues. If that is the case, then that would seem to point to problems with the turn signal switch. I still can't figure out how turning the lights on factors into this, though.

Just for kicks, have you checked the headlight switch for any extra (added) wires?

None of this would seem to affect the backup lights so it appears you have two separate issues.

I have not replaced a TS switch but many on here have. Do a search or wait for others to comment.

I have found that the forum search doesn't like me for some reason. I have had much more success by Googling something like this:

fordification turn signal switch

You'd be surprised how well that will work at times. It can reveal some very interesting results . . .

[reeshard08]

So when I was installing the wire harness from the engine bay back to the tail lights I noticed there is no wire going to the transmission, leading me to believe that it is either missing, or I am missing the neutral safety switch on the steering column, solving my reverse light problem. I have an automatic tranny by the way. I ordered a new TS switch, so hopefully that will fix a few problems, but I also took out the instrument panel and discovered a mess of spliced wires and things not being hooked up (probably a bypass of the NSS to get the truck to start). Is there a diagram available that shows what color wire goes to what back there? Some of the, what seem to be, original wires from the harness go through the firewall, into the engine bay, but some of them are not hooked to anything. I'm kind of overwhelmed by the number of wires that are either not hooked up or spliced. I have the wire schematic for the entire truck, but it only has colors, no what they go to.

[68RGR]

There are schematics on this site but the detail is a bit different for each year. The colors are listed by the number on each wire. Try to identify the unconnected wires first. Some of them are meant to be that way due to various options and to give you a place to connect to a power source. Then check the spliced wires to see that the splices are safe and secure and to verify that the spliced wires are supposed to be connected together.

It could be that there was a significant electrical issue (read: fire or close to it) once that damaged some of the wiring. That could explain the splices.

Of course, it's also possible that some poor, uninformed soul butchered the harness while searching for who knows what.

It is easy to be overwhelmed by LOTS of wires. But, if you really want to get things straightened out, you have to take it one wire at a time. Try using some masking tape to label each wire. That helps me get back to just being "whelmed" sometimes.

I prefer to use solder and heat shrink tubing to get a reliable result when repairing these wires.

You can do it - It's just a matter of time and being dedicated to getting it right.

Good luck!

[RustRed]

WHAT WAS THE PROBLEM. WHAT WAS THE FIX???

[reeshard08]

So after the whole ordeal the culprit ended up being a bad ground on the connection between the driver side taillight bezel and the body. It was connected and gave off a faint enough continuity on the mulitmeter to be overlooked. Scraped away some paint, reattached and it lit right up.