68 tail light problems.

[Milo]

Hey all -

I'm having some problems with my tail lights - basically nothing is working properly, most not at all.

I went out and picked up some new bulbs - 1157's - and they're a bear to install, when the even fit.

Anyway, after installing the new bulbs, all the running lights were working on the drivers side and the passengers side were on, but faint compared to the drivers side. Blinkers weren't working, nor were brake lights.

I decided to remove the whole panel and see what was going on inside... mistake #1.

I then moved inside the car and started tinkering with the blinker switch. I swapped out the blinker can with a new (553) and cleaned up the contacts on the turn signal switch. They are now functioning - I hear the can clicking and they work on the front lights as the all should (individual blinkers and hazards)...

What's really strange is now none of the running lights work. When the hazards are on, the three passengers bulbs flash and the inner drivers side does as well. What's even stranger is when an individual blinker is engaged, the same thing happens. 3 on the right and 1 on the left, regardless of which blinker is used. This could have something to do two wires that were cut and tucked - a thicker black and a regular red - that I tried reconnecting to each other.

So, does anyone have wiring diagrams for the whole back tail light section? I'm flying blind here and am totally confused looking at regular mustang wiring.

Extra points if someone knows what in the heck is going on and has a solution!

Milo

[Krelboyne]

Cougars Unlimited has this troubleshooting guide on his site. Specific to 1968 Shelby Mustang. Might get you started.

http://www.thuntek.net/cougars_unlimited/smseqts.htm

[TLea]

95% time. Bad grounds

[Milo]

I spent some time working on cleaning up the sockets (thinking it was a grounding issue) but they are pretty well aged. I'd much rather save what was original - especially the original dynamite sticks - than go reproduction. Is there a good way to restore the sockets without cutting and splicing?

[Milo]

Would the 553 account for the failure of running lights?

[Cobrask8]

I also have years of fixing these cars. All above have identified many of the common problems.

Clean sockets, and check socket wiring

GROUNDS!!!!!!!!!!!!!!!!!! Super critical. Clean the main ground in the trunk from the taillight panel

Check all functions with either the engine running or a battery charger on and operating. Without that, the voltage will be low, and the lights will not work properly.

ENGINE GROUND - MUST have a clean cable to block connection, and a battery to chassis ground it CRITICAL! If you are missing the braided strap at the back of the motor, things will never really work right. If you are not concours, add a ground from the battery directly to the body. In Class, we always teach the "Grounding Triangle" Also makes your car start better.

Keep us posted, ask questions.

[Milo]

There's a ground from the tail light panel to the trunk? Does anyone have a picture of that?

[Cobrask8]

right on the center rear part that protects the gas fill and trunk lock, usually the wires mount on the pass side. Too many people paint it real nice, so a good ground is never made. Scratch off paint down to metal, clean everything, re-attach

[Royce Peterson]

Great advice. Also the ring terminal for this ground wire has a serrated washer that goes between the terminal and the body to insure a good electrical circuit.

right on the center rear part that protects the gas fill and trunk lock, usually the wires mount on the pass side. Too many people paint it real nice, so a good ground is never made. Scratch off paint down to metal, clean everything, re-attach

[Milo]

Update -

I tested the brake switch at the pedal and was getting 12v constant from the green/red, but nothing from the green when the pedal was depressed. So, I hopped in the car and drove over to NPD to pick up a replacement. After getting the new one installed on the pedal, I went to install the extension, first to the switch and then to the under dash loom. Of course, the wires broke at the under dash side of the connection. So, now kind of sidelined.

But here is a question or two - shouldn't I be getting brake lights if I connect the green/red and the green? What is stranger is that I seem to be getting 12v from both of the wires individually. Shouldn't I only get 12v from the green if the circuit is completed at the brake switch?

This is making me think that there is something happening at the turn signal switch that is only effecting the running/brake lights. As the car currently sits, the turn signals are functioning (sort of). Theres a wonky connection happening at the outer and center lights of the drivers side. The inner functions great, but the out is dim and if I even put a bulb in the center the outer stops working... and the center just doesn't want to work. Upside is the original dynamite stick is working as it should.

On the passengers side, all three lights are functioning, albeit dimly compared to the inner of the drivers side. BUT they are all flashing at the same time which makes me think the dynamite stick on the passengers side is done.

I removed and cleaned the ground at the back panel.

I'm getting pretty antsy to break int his engine and the no brake light thing is really wearing on me!

[Cobrask8]

Milo,

You are going through a "Rite of Passage" most 68-70 owners have gone through with the sequential and rear lights. Ask any owner.

Yes, you have identified another common problem - the turn signal switch in the column. Replace that. The contacts do burn/corrode, as the extra lights draw up to 3X the original design parameters of a single standard Mustang taillight. Any other questionable wiring, replace that too.

PM me your e-mail, I'll send out that article from Hemmings I wrote all those years ago.

Don't give up.