68 GT350 Tail Light Issue

[Corey Bowcutt]

I have a problem with my tail lights that has been there since I bought the car I just did not know it.  The tail lights work just fine by themselves or with the blinker on.  The brake lights work fine by themselves or with the blinker on.  But when you have the tail lights on and you apply the brakes the tail lights intermittently turn on and off all together. I have noticed since I bought the car that when I drive at night and come to a stop the dash lights turn off and on randomly.  I did not realize until yesterday that the tail lights turn off and on when the dash lights turn off and on.  The head lights are not affected by this.
Today I disassembled the tail lights and many of the sockets for the 1157 bulbs were in bad shape.  I repaired as best I could and do have all the lights working but they still intermittently turn on and off when both the tail lights are on and brakes are a applied.
I have always noticed that my sequential light sticks work kind of odd in the fact that when I apply the brakes the tail light turn on sequentially like they do for the blinker.  I do not believe that is correct?
So I am going to buy a new tail light harness and sequential light sticks but has anyone ever seen an issue like this and determined its caused to be something I have not considered?  Any help is greatly appreciated.  I hate electrical issues.
Thank you, Corey

[gt350shelb]

the brake lights do sequence  with original  dynamite sticks .

I have had some issues with  the sticks  working on some bulbs  sometimes

Every connection  from the turn sinal switch to the bulbs needs to be  very clean .

I also added extra grounds to each light socket   to make them brighter.

I found out how bad the grounds were  when i burned my finger on  the ground strap in the trunk  near the fuel filler neck 

[papa scoops]

as above. seq brake lites. make sure he ground wire is clean on both body and connector, double check and clean the park lites also. have some one help you check, if something doesn't work, jiggle the wires till it does.   ARR! jiggle the handle, it'll flush! phred

[Builder 2]

My convert is a driver, we converted mine to led circuit board. Works great and is safer with brighter lights, haven't had any issues since.

[shelbydoug]

I put in a solid state system from East Texas Mustang parts. It fixes all of these issues Phil refers to and people can actually see them work in the sunlight.

There is one shortcoming. One.

They took out the brake quick sequence flash. The builder was told that it was not an original feature.

Ironically he told me that it took a lot of work to make the brakes stop quick sequence flashing.

Other then that, install this kit. Leave the dynamite sticks hanging in there but not hooked up.

[Cobrask8]

All above are correct

In addition, if everything blinks, replace the headlight switch.

I agree about the grounding problem. In Auto-Shop, I teach my students about the "Grounding Triangle". A three way ground between battery, chassis, and engine. If you are missing any one of the three, and/or your existing connections are dirty/painted/terrible, you will have the blinking lights. So many restorations make everthing look great, at the sacrifice of functionality. Add the extra wire from your battery to the uni-body. Do you still fabe the braided strap from the rear intake to the firewall? Neg batt cable to engine block - NO PAINT on the connection and wire-brushed clean? That connection being bad will also give you starting problems.

And on the Plus side, how good is your battery? Alternator output and regulator performance. If you are just barely making voltage, and sudden drain will also result in the dimming result you see.


Break out the meter and start checking everything.

[shelbydoug]

All above are correct

In addition, if everything blinks, replace the headlight switch.

I agree about the grounding problem. In Auto-Shop, I teach my students about the "Grounding Triangle". A three way ground between battery, chassis, and engine. If you are missing any one of the three, and/or your existing connections are dirty/painted/terrible, you will have the blinking lights. So many restorations make everthing look great, at the sacrifice of functionality. Add the extra wire from your battery to the uni-body. Do you still fabe the braided strap from the rear intake to the firewall? Neg batt cable to engine block - NO PAINT on the connection and wire-brushed clean? That connection being bad will also give you starting problems.

And on the Plus side, how good is your battery? Alternator output and regulator performance. If you are just barely making voltage, and sudden drain will also result in the dimming result you see.


Break out the meter and start checking everything.

Sure. Today you get it working with clean grounds. Tomorrow...forgetabodit!

[Bob Gaines]

All above are correct

In addition, if everything blinks, replace the headlight switch.

I agree about the grounding problem. In Auto-Shop, I teach my students about the "Grounding Triangle". A three way ground between battery, chassis, and engine. If you are missing any one of the three, and/or your existing connections are dirty/painted/terrible, you will have the blinking lights. So many restorations make everthing look great, at the sacrifice of functionality. Add the extra wire from your battery to the uni-body. Do you still fabe the braided strap from the rear intake to the firewall? Neg batt cable to engine block - NO PAINT on the connection and wire-brushed clean? That connection being bad will also give you starting problems.

And on the Plus side, how good is your battery? Alternator output and regulator performance. If you are just barely making voltage, and sudden drain will also result in the dimming result you see.


Break out the meter and start checking everything.

Just to add , something that is commonly left off but from the factory the grounding points typically got a star washer which would dig into the metal for better ground.

[Corey Bowcutt]

Today I finally fixed my tail light/ dash cluster issue.  I work for a large defense contractor and am a mechanical engineer and electrical things sometime freak me out.  I went to the best trouble shooting electrical engineer I know at work.  I have seen this guy trouble shoot amazing problems on multi million dollar airborne laser systems so i figured it was worth a try.  He is not a car guy at all and probably can not even spell Shelby but circuits are circuits.

He he sat down with me for about 1.5 hours and I explained the symptoms and what I had done to remedy them.  He poured over the electrical schematics I have for the car.  I bought a complete Ford 1968 wiring and vacuum diagram manual from Jim Cowels last year and it really paid off.  He studied the multi sheet schematic and after 1.5 hours said it has to be the head light switch.  He said that is the only common component between the tail lights and the dash cluster. 

I was a bit skeptical but a new switch was only $30 so I purchased one.  Today I installed it and to my great surprise the problem is gone.  The dash cluster no longer goes out when I have the lights on and come to a stop.  It has done this since I bought the car 2.5 years ago.  The tail lights stay on regardless of what else is on.  The turn signals also work as they are suppose to.

I did replace the flasher as well after I replaced the switch because it seemed the last bulb to the far outside did not light up well.  The flasher in the car was the right one but when I replaced it with the one I bought on Ebay the lights worked even better.

i love a happy ending!

[Steve McDonald Formally known as Mcdonas]

Glad to hear it.

[kjspeed]

I thought I would add my experience to this thread as I was having problems with my right turn signal. Since I had replaced both dynamite sticks with repops a few months ago I began with the assumption that there was a bad ground. I started with the easy stuff first; the ground wire attached near the filler neck and cleaning the contacts from the dynamite sticks to the light sockets. I put a star washer on the ground point and cleaned some paint overspray and general gunk off the terminals on the connectors but still had weak/intermittent right turn signal.

Next up I removed the bezels and lenses and checked the lamp sockets and lamps. All good there so I had to figure out how to check the actual ground for the light assembly. I removed the bumperettes and rear bumper, then took off the fiberglass light panel. When I flipped it over to look at the back side the right light housing ground wire was loose as a goose because the screw had backed out. So I put a star washer under both the left and right ground screws and plugged the lights back in and everything worked properly.

I have to say, it's not the easiest grounding point to get to but I'm glad it's fixed anyway - hopefully for good!

Since I was on a roll I decided to connect the wires to the trunk lid light which were disconnected when I bought the car. I found a pigtail by the right wheel housing but it was only hot when the doors were open. That's where I connected the trunk light and it works fine, but only if the doors are open and the other interior lights are on. Is this how it's supposed to be? I don't see any place for a switch on the trunk lid.

~Kevin

[Bob Gaines]

I thought I would add my experience to this thread as I was having problems with my right turn signal. Since I had replaced both dynamite sticks with repops a few months ago I began with the assumption that there was a bad ground. I started with the easy stuff first; the ground wire attached near the filler neck and cleaning the contacts from the dynamite sticks to the light sockets. I put a star washer on the ground point and cleaned some paint overspray and general gunk off the terminals on the connectors but still had weak/intermittent right turn signal.

Next up I removed the bezels and lenses and checked the lamp sockets and lamps. All good there so I had to figure out how to check the actual ground for the light assembly. I removed the bumperettes and rear bumper, then took off the fiberglass light panel. When I flipped it over to look at the back side the right light housing ground wire was loose as a goose because the screw had backed out. So I put a star washer under both the left and right ground screws and plugged the lights back in and everything worked properly.

I have to say, it's not the easiest grounding point to get to but I'm glad it's fixed anyway - hopefully for good!

Since I was on a roll I decided to connect the wires to the trunk lid light which were disconnected when I bought the car. I found a pigtail by the right wheel housing but it was only hot when the doors were open. That's where I connected the trunk light and it works fine, but only if the doors are open and the other interior lights are on. Is this how it's supposed to be? I don't see any place for a switch on the trunk lid.

~Kevin

The trunk light feed should have constant power. The switch is built into the light socket .It is a mercury switch .When the lid tilts up the liquid mercury sealed inside flows across both inside contacts making a contact and causing the light to turn on. 

[kjspeed]

Thank you Bob. There is another pigtail in the same area, I'll check to see if that one has constant power.

[Cobrask8]

Shelbydoug noted about the sequential not being original equipment.

There is a document floating around (I have a copy) from Ford/Shelby about how to disconnect the sequential system in certain states. Seems back then the sequencing of brake lights was not permitted. So, states including NY, Florida, and possibly others had the dynamite sticks removed by the dealer before the cars were sold.

So, not all 68's had the sequential feature originally!

[Bob Gaines]

Shelbydoug noted about the sequential not being original equipment.

There is a document floating around (I have a copy) from Ford/Shelby about how to disconnect the sequential system in certain states. Seems back then the sequencing of brake lights was not permitted. So, states including NY, Florida, and possibly others had the dynamite sticks removed by the dealer before the cars were sold.

So, not all 68's had the sequential feature originally!

I agree with the concept but If you think that everyone that was supposed to be modified was (or even a large percentage IMO) I think you are being overly optimistic. It was probably only done if someone complained .Just my opinion.