Topic: 1967 Turn Signal and Emergency Flashers Messed Up

[kkupec02]

I just bought the car mid March and had a burnt horn contact so I had to change my steering wheel harness. Never got the car on the road yet due to brake rebuild needed so it immediately went up on blocks. I thought that I checked turn signals and emergency flasher and believed that they worked before the swap, but evidently not. I got a repro harness and installed it. I got a strong left turn signal. Weak right turn signal you can see in daylight, but also only evident in the dark, a very weak left turn signal at the same time. So the power kind of bled over to the left on a right turn signal. Flashers give me a strong left hand flash but you can't see anything on right except a very weak right flash only evident in the dark. Right hand side issues are both front and back identical. So it's the whole right hand side. I paid $200 for a new in box Ford 1967 harness, installed it and got the same thing. Where should I start the diagnostics? It must be something going on right hand side. A short? A bad ground? Thanks.

[67gta289]

What do the brake lights look like - even in brightness left to right?  That can help rule out a ground problem.

[kkupec02]

My booster and master cylinder are out for rebuild. So my brake switch is not attached to the booster rod right now. My wife pulled out a couple of pictures from March as the car hauler took it off the truck at night. The left brake light is strong, the right brake light is noticeably weaker. Any particular place to look for a weak ground? I will have to look at my wiring diagrams. I assume the wires are routed through relays and voltage regulator? thanks.

[kkupec02]

ps I have a 289 GTA coupe from San Jose as well.

[jwc66k]

Do you have a set of the Osborn Products 67 Mustang Assembly Manuals? The electrical manual has a fairly good set of drawings and schematics. If not, get a set. The 67 Mustang set is the most complete.
Jim

[kkupec02]

Thanks. I do have the set as well as the 1967 shop manual

[kkupec02]

That's next on my list to peruse through.

[67gta289]

It does sound like a ground problem to me, so let's rule it our or fix it.

You should find the common (left and right hand side lamps) ground screw on center sheet metal support in the trunk where the latch is attached.  That ground should be good since one of your lights is bright.

Pull the 57 black ground off the male spade connector on the weak light.  Temporarily connect a wire from the spade to the ground screw.  I typically have several jumper wires with alligator clips for things like this, hopefully you can find something handy that works.

If the light is bright, your problem is with the female spade connector, or internal to the backup light connector, or at the ring lug connector (crimp) at the ground screw.  You could also have a section of wire under the insulation that has multiple broken strands, which is harder to diagnose and find.

If the light is still dim, the problem is in the socket.  I would swap bulbs, left and right, to see if the problem clears.  If not, inspect the socket closely, you might have some corrosion in there.

By the way, the 14305 and 14290 numbers on the diagram represent basic part numbers for the two wire harness assemblies.

[kkupec02]

I listed this as a regular 1967 problem as electrical should be similar between a Shelby and a Mustang. I am having problems with my Shelby. I attached a few pictures of my electrical. I cleaned the common ground near the trunk latch and as you said, no difference. I then checked the volts going to the good left side and it was receiving a relatively steady 0-1.0 volts up and down. I checked the bad right side and the volts were jumping all over from 0-2.6 volts. There seems to be only that trunk latch ground in the back on the Shelby's. All black wires come from the front and only ground there in the back. That ground branches to the right and left side in the back. There is no individual ground for each socket/side on the Shelby. I wonder if it is my voltage regulator? It seems to be an older "electronic" replacement?   

[jwc66k]

I then checked the volts going to the good left side and it was receiving a relatively steady 0-1.0 volts up and down. I checked the bad right side and the volts were jumping all over from 0-2.6 volts.

In a 12 V system? What am I missing here?
Jim

[kkupec02]

It's factory 12 volt. Not sure why I am seeing spikes. Can't be regulator as it comes from front and branches to both rear lights. Should be a problem with both not just one side if it was regulator. Remember, I am having bleed over issues and weak signal on the front right side as well as the back right side. Yet the same wire from front is used on both rear lights. Also, why do I have problem in front right side as well?

[kkupec02]

Just checked rear tail lights again. Left working strong pulling 0 to 1.2 volts with bright light. Right weak lights yet pulling 0 to 3.0 volts bouncing around with even some negative readings thrown in. When I turn on left signals, no problems. When I turn on right signals, weak back light and front light weak with bleed over to left front signal as well. ie, right turn signal turns on right back, right and left front..

[67gta289]

The turn and emergency signals are a relatively slow frequency square wave, and this is where an old analog meter is superior to indicating what is going on.  It is the sampling rate and update time on your digital meter that is not telling you what is really going on.

You will see at each bulb two wires - the black wires are the ground (57).  Do the wires jumper from bulb to bulb?  From the outboard bulb, does it then, like the Mustang, tie into the circuit that includes the backup lamp? 

If you can install a jumper, like I recommended, from the ground screw that you cleaned up, to the bulb socket that can help you determine if there is a poor ground between the lights and the ground screw.  From the looks of it, that might be difficult.  I would probably pull the inboard most lamp, pull the bulb, and probe the ground pin, with an alligator clip connected to the ground screw, and then see how bright the lights are.

The other option is to pull all of the bulbs and connectors, and give them a good cleaning.

[kkupec02]

The main harness comes in from the drivers side, left. It branches into 3 parts. One part down to left back up light. One part to left turn signals. One part across trunk to right turn signal. Then that branches to right back up light. Turn signals are on a chain. The wire goes from outer, middle inner with same wire from harness on each side. So the wire jumps from bulb to bulb. I pulled off one of the right tail light sockets. The other 2 got immediately brighter. I did this to each of the 3. It made the other 2 brighter each time. I jumped a wire like you said from the trunk ground to each bulb socket. It made no difference. Remember that all through this, the right signal light continued to turn on both the right and left FRONT turn signals at the same time. I pulled all 3 sockets on the right rear. I'll clean the sockets and replace the bulbs just in case. Maybe they sell replacement sockets as well. I then tried the right turn signal with all 3 bulbs out of the harness. No change. Right signal still turned on both right and left FRONT turn signals. 

[67gta289]

Does this have sequential taillights?  If so I would temporarily bypass that to remove it from the troubleshooting process