Hi Gang,

I have an electrical issue. 1966 Dart GT /6 225. My brake lights don't work (the stop/brake/tail lights remain on and do not increase in intensity upon applying pressure to the brake pedal). All of the other lights (backup lights, turn signals, etc.) in the vehicle work properly. All of the contacts are clean and not corroded.

I replaced the stop lamp switch about 2.5 years ago and, thinking it went bad, installed a new one the other day to no avail. I even tried switching the leads thinking I had somehow gotten them mixed up. I have a 3rd switch one on order that should be here in a few days.

From this post...
http://www.slantsix.org/forum/viewtopic.php?t=5500

and the comment from Chuck...
"Use a circuit tester to check both sides of the brake switch. One side should always be hot and the other side should be hot when the brake is pressed. If that works, the problem is most likely in the turn signal switch. Check both turn signals with brake on and brake off and report your findings."

I have a multimeter, but I have never learned how to use it yet. Which lead should always be "hot"- the white lead or the one with the two pink wires? What am I testing for- DC voltage?

FYI: I also have the wiring diagrams.

Thanks,

Tom

The wire that should be hot all the time is the one coming from the flasher unit or fuse block. The other wire going to the turn signal switch should only have power when you step on the pedal. Yes, DC.

Did someone force the stop/tail lamp bulbs into the sockets backwards? 180º off? It can be done. This will make the brake filaments light up when you turn on the tail lamps. And when you apply the brake pedal the tail lamp filaments will light but they are dimmer than the brake filaments so it will appear that they are not getting brighter.

I am confused about "the stop/brake/tail lights remain on". With the head/tail lights off, are the brake lights on? What happens when you step on the brake?

The pink wire should be the "hot" one. Set your meter up ro read DC volts and hook the black wire to a good ground. Connect the red meter wire to a good 12v source (hot) just to verify that the meter works. Now connect the meter's red wire to the pink wire of the brake switch. You should read 12v. If not, check fuses with a meter!! They sometimes look OK and are not. Next hook the red meter wire to the white brake switch wire. There should be 0v there when the brake is not pressed and 12v when the brake is pressed. If not, bad switch.

_________________
Chuck Rivers, Webmaster

The brake lights come on with the headlights. Nothing happens when I step on the brake- therein lies my issue.

The only way I think that can happen is if the wires are shorted or the bulbs are installed wrong as mentioned above. There is nothing in common with the brake and tail lights except the socket. The brake light circuit does not go anywhere near the headlight switch.

_________________
Chuck Rivers, Webmaster

Hi All,

I tested the stop lamp swith (per Chuck's advice) and it checks out OK. This is expected as it is a new switch.

So the probelm is _not fixed_. Here's the scoop...

1. When I turn the ignition key to the right (with the headlights off... although it shouldn't matter) and press the brake pedal, the brake lights do not work, the turn signal indicators work fine.

2. If I turn the headlights on... all 4 lights in the back come on, pushing the brake pedal causes no response whatsoever, the turn signal indicators work fine.

As a check, the bulbs in the outer taill light housings have 2 filaments while the inner ones have one filament so this is not the problem either.

I'm clueless. What can I test for next?

Note: If I take a while to respond to this post again, it is because I have to go to Chicago for a few days and I have a kid due in 2 weeks.

Thanks,

Tom

The culprit could be your turn signal switch. On cars with combination red rear brake/turn signal lamps (almost all of our slant-6 cars in North America have this system, except for certain-year F-bodies), the brake lamp feed goes through the turn signal switch. With the turn signal lever in "no turn" position, the turn signal switch simply passes current from the brake lamp switch directly back to both brake lights. Move the turn signal lever to the "right turn" position, and the shuttles in the turn signal switch changes the source of the right rear combination lamp's power from the (steady) brake lamp switch to the (pulsing) turn signal flasher.

The shuttles and contacts get worn with decades of use, and eventually they no longer make contact. To test if this is the case, set your multimeter to DC volts. If you need to set the range manually, choose the range closest to "20 volts". It may be 30 or 40 or 50 rather than 20. Connect the black lead to a good ground. Remove both wires from the brake lamp switch and connect the red multimeter lead to each brake lamp switch wire in turn. One brake lamp switch wire should always be "hot", that is, when you touch the terminal with the red lead, the multimeter should display battery voltage (between 12 and 13 volts). The other wire should give a "0" result. If you don't find an always-hot wire, you've got problems upstream of the brake lamp switch. Check your fuses; the brake light wires may have chafed on a metal edge in the trunk and caused a short circuit, blowing the fuse. If fuses keep blowing, you'll have to trace and find the short circuit to fix the problem.

Assuming you did find an always-hot wire, now let's test the turn signal switch. Under the dash, there's a rectangular multi-wire connector made out of transluscent or black nylon. Half of the connector is attached to wires that come out of the slot in the side of the steering column; the other half attaches to matching wires that come from the under-dash wiring harness. Lift this connector's locking tab and pull it apart. We'll be working with the half of the connector that is connected to the under-dash harness, not the half that's connected to the steering column wires. There will be a dark green wire and a brown wire right next to one another at one end of the connector. These are the left and right rear combination lamp wires. Carefully use a jumper wire to connect the "always hot" brake lamp switch wire to these two wires, the dark green and the brown. If the brake lamps light when you do that, then replacing the turn signal switch assembly should clear up the problem for good.

Just to clarify for you how those two-filament bulbs work: One filament is 8w. It is the dim filament used for the dim red taillamp function. The other filament is 27w. It is the bright filament used for the bright red brake and turn signal functions.

The fact that the brake lights come on when the headlight switch is on would seem to me to rule out the signal switch, since the headlight power does not go through it. Somehow power is being shorted from the headlights to the brakelights. Remove ALL taillight and front signal bulbs, then test each terminal in the sockets for voltage with the headlight switch on. You should get ~12v on only one of each of the bulb socket terminals. If, for example, you get 12v on BOTH of the terminals in the brake light sockets, then there is a short in the wiring somewhere. If all checks out will ALL bulbs removed, then re-install bulbs ONE AT A TIME and test again. This doesn't explain condition #1 in your post, but it is a place to start.

_________________
Chuck Rivers, Webmaster

No, I'm not convinced that's the case. I think the original poster was writing a little confusingly about the two different intensity levels available from the outer compartments of the rear lights. He said " If I turn the headlights on... all 4 lights in the back come on, pushing the brake pedal causes no response whatsoever, the turn signal indicators work fine.". That tells me that his four TAIL lights, and not his two brake lights, come on when he turns on the headlamps. And that's as it should be. That also tells me nothing changes when he steps on the brake pedal, which is the "broken" part—the outer two lamps should get bright, and they don't. But we also know from this that the outer two lamps DO flash bright when he operates the turn signals, which tells us the turn signal circuit and the brake/signal filaments in the outer bulbs are OK.

Sorry, Dan. My bad! I forgot that there are 4 taillights in the '66. You are right. That means checking BOTH sides of the brake switch for power when the pedal is pressed. If there is power on both sides of the switch, then I agree that the trouble must be in the signal switch. Sorry for the confusion, Spazus.

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Chuck Rivers, Webmaster

this might be way off, but i had a problem like this but reversed on my 73 dart. somehow, the switch or what not under the dash had gotten bent enough that the brake lights stayed on all the time. maybe yours is bent enough that the switch isnt being activated?

seems way to simple and i might have missed it being stated above, but its worth a try.

Hi All,

After following Chuck's and SlantSixDan's advice, I was able to determine that my stop lamp problem was due to a faulty turn signal switch. I ordered one from Layson's and managed to get everything working so we are good to go. Thanks a lot. This forum is wonderful.

FYI: The turn signal switch that came from Layson's is a tight fit in a 66 Dart (the tolerances for the molded nylon parts were not that great- a quality control issue) and required some additional work to get it in. Seems to work fine though.

I'm legal once again.

T.

You can save a lot of money if you remember that for most "functional" parts (mechanical, electrical, etc.) Layson is just buying plain old ordinary on-the-shelf parts and marking them up (WAY up). That switch is almost certainly a Shee-Mar SM106, which is made in Longmont, Colorado by Shee-Mar. It's a slightly different switch than the original, and does require some trimming to fit in '62-'67 columns (fits fine in '68).

I'm curious...what'd Layson ding you for on it? $

Don't fall over but I paid $98 for the turn signal switch. I know Layson's is on the pricey side. I had already replaced the switch a year of so ago with a used one I found up at Wildcat's (who are very nice BTW) but it didn't hold up very well. To be honest, I'm just sick of various turn signal switch problems over the years and was willing to pay just about anything to get it resolved. Time is money and I have little time these days. With a kid on the way I have little money either. Nonetheless, I did manage to send in a contribution towards hosting the slantsix.org website year. We should apply for non-profit status and possibly get some serious donations rolling in.

This board is wonderful. I prpbably would have sold my car a few years back if it weren't for you guys. Much appreciated.

Tom