Odd brake/tail light problem

Hi All,

First off, let me just say that when I finished putting this ugly 1973 Dart Sport 340 together a month ago, all of the lights worked the way they should (and when they should). I have done nothing but race the car at the brackets for about a month, once a week. That is to say, the car is only loaded on and off the trailer and then beaten on.

It finally got dark early enough so that we needed to run tail lights and suddenly mine aren't working correctly. When I pull the light switch knob, to either "parking" or "on" position, what I believe to be my brake lights are coming on - both seem very bright . Nothing changes when I depress the pedal. With the lights "off," the brake pedal is not activating the brake lights whether the key is "on" or "off."

When I turn on the light switch with the left turn signal on, sometimes the left signal indicator on the dash holds a steady green arrow. Sometimes not. The right turn signal operates the front signal only.

- All front lights and rear running lights and license plate light work properly.
- Reverse lights work properly.
- There is a designated ground running to the back of the car and, because some of the lights back there work, I don't believe the problem to be in the back of the car.

Is it possible for the brake light switch on the pedal to affect the turn signals?
Is it possible that I am mistaking my very bright tail lights for brake lights and the problem is only in the brake light circuit?

You can see what I mean by "seem too bright to be tail lights" in this video - they're shining on the track:


Electronics are my worst subject.

Thank you in advance!

Here's where I'd start. I assume, is it? a factory harness?

Disconnect the rear harness at the left kick connector. Get a diagram (You can download wiring diagrams and or service manuals from MyMopar) "Rig" a alligator clip to power THROUGH A TAIL STOP LAMP in series so that it will limit the current.

Now apply power to each of the rear lamp terminals and verify they work. Tail, left, right, and reverse

If that all works OK, now take your "test" stop/ tail lamp and ground the end you had hooked to battery and use it for a test lamp. This time, access the lamp pins in the front kick panel connector and see if the output power is what you'd expect, in other words tail, stop, left, right turn.

Take a length of elec wire, strip each end, use vice-grip or similar and clamp one end to trunk lock striker.
Take the other bare end, and touch it to the "socket or bulbs base" of the offending lights.
If they begin to act as they should, repair the grounds as nec.
There may be a ground screw(s) on the inside lower edge of the trunk, where the harnes lays.

As it is now, I believe you'll find, the park lite electricity is going to the bulb, but can't ground, so juice goes back up the brighter brake filiment (both filiment are likely lit) up to ground the circuit thru the indicator bulb in the dash that is also lit .
Good luck .

It means you’re fast with your brakes on !

Yes - it is the factory harness.

67Dart273 said:

"Rig" a alligator clip to power THROUGH A TAIL STOP LAMP in series so that it will limit the current.

Click to expand...

67Dart273: I'm not sure how to do the above

I tested several spots with the multi-meter:

1) Coming out of the rear light wiring harness with headlights ON:
a. Black tail light wire = 11.4v
b. Brown (right side) brake light/turn indicator = 0
c. Green (left side) brake light/turn indicator = 0

2) Coming off the brake switch
a. front tab = 0 (with or without brake applied)
b. back tab = 0 (with or without brake applied)

With the harness disconnected and the lights on, I was able to jump the black tail light from the front harness terminal to black tail light on the back harness terminal and get the "bright" tail lights to come on.

Thinking this would be a source of constant power, I left it connected in front and tried both brake lines (brown and green) and got nothing. Also, tried the pink reverse lights, which I know work just fine - they didn't come on either. So I may be doing something wrong.

Aaaaand.... running back and forth between the computer and the car I just locked the keys in the ignition. Dammit.

Okay - got back to the car today with a clear head.

Changed out both tail/stop bulbs with new ones that are confirmed working. I tested the old ones and, for some reason, both bulbs' tail light filaments did not work. They were new. What's going on there?

I ran jumper wires from both tail/stop light housings to the ground by the trunk striker, which also has an extra 12 gauge ground wire back to the negative pole of the battery. There is lots of extra grounding back there.

I made up a wire and ran 12v from a keyed source (where radio was, I think) and tried each of the following three blades on rear light harness, one at a time:

1) Tail lights = came on (normal, not-too-bright)
2) right stop light = came on (bright)
3) left stop light = came on (bright)

Now... after I plugged the wiring harness back together, the tail lights are working (and I was right, it WAS the brake light filament coming on before) and the turn signals are working, sort of: the turn signals flash at increasingly slower rate if I turn on the parking lights (slower) or the headlights (slower still).

Brake lights still don't come on from brake switch application.

So I tried a different brake light switch. I mounted it on the door frame and grounded it, then plugged it into the wires coming out of the dash. Nothing. I switched the wires and still nothing.

Working my way back one step, I put the multimeter on each of the disconnected wires that connect to the brake light switch. No voltage to either of them.

Thoughts?

The brake light switch should have power at all times regardless of key on or off. So from there it is a simple matter of chasing the circuit back to the fuse panel

In the meantime in order to check that brake lights power is getting through the TS switch, you can jumper 12V into the brake switch wire that feeds to the TS switch, I believe it is the white

Make sure the bulbs and the pigtail contacts are indexed properly in the sockets. When sockets get rusty, or pigtail insulators become damaged, they can twist in there and not make proper contact.

I assume you know how 1034/ 1157 bulbs work. The shell is common, one contact is tail, the other brake.

I don't know why two (new?) bulbs would be blown, unless poor quality, or maybe the charging system is over voltage?

I have had two new bulbs with one bad filament in each several months ago. Drove me crazy. Can't trust new Chinese bulbs.

Problem solved! At least, temporarily.
I did as you suggested and tested the brake switch with power - it works.
I unscrewed the fuse box mount to get a better look as I followed the pink wires back and found... the palm of my right hand slapping my forehead. Nikolai Tesla over here seems to have missed the fact that there was a blown 20A fuse. I SWEAR I looked closely at the fuses first and did not see one blown.

But now everything is working as it should except for one small thing: the left blinker is still much slower than the right when key is on but engine is off. With engine running, all is normal.

Thank you all so much for your help. I have no idea why the fuse blew in the first place and will keep an eye on it, as well as keep some spares in the glove box. And now I know that the brake lights are on a different circuit than the others, too.

Some things to keep in mind. These old fuse panels. if the fuse clips are rusty/ corroded or loose, they will not make good connection with the fuse and this will cause HEAT at the terminal. Heat is what blows fuses--so current through the circuit + generated heat at poor clip connections can blow the fuse with way less current through the circuit than rated.

67Dart273 said:

Some things to keep in mind. These old fuse panels. if the fuse clips are rusty/ corroded or loose, they will not make good connection with the fuse and this will cause HEAT at the terminal. Heat is what blows fuses--so current through the circuit + generated heat at poor clip connections can blow the fuse with way less current through the circuit than rated.

Click to expand...

For sure. We drove w/o AC for many summers in Florida in our ~1971 AMC Matador Station Wagon because the blower stopped working. My dad had checked the fuse and it looked fine, so he gave up as "too expensive to fix". Years later, a guy at work seeing him wet with sweat mentioned that the fuse might have melted from corrosion heat. Sure enough, the wire was melted inside right at the tip where you couldn't see it. He then installed a resettable breaker instead which the guy mentioned and we had AC. Today, we have free multimeters (Harbor Freight coupon) and web info like this to help. He could have tried swapping fuses, but perhaps Chemistry grads don't think of such things.