Funky brake light problem - please help me troubleshoot!

[NATEandALLI]

Bronco in question is my wife's 73 that we converted to 2wd. You can see some of the build here: https://classicbroncos.com/forums/showthread.php?t=292116

The main problem is that the left brake light does not work in most instances. There are only two times the left brake light works as it should and I will describe those instances below. I tried to be as analytical as possible and tested a bunch of different things to try and narrow down the funky behavior.

First, let's go over wiring. My father-in-law modified the column and converted it from manual column shift to auto floor shift. He cut off the connector to get the wiring through the column and then I repinned both sides with a new 8 pin connector. I'm confident I did everything right but decided to check anyways. See speadsheet screen shot below.

 

[NATEandALLI]

So here are the different tests I did.

Head light switch first position, all parking lights work including left and right tail lights

All the following tests with the brakes on is with the brake switch disconnected and a jumper across the two pins.
Brakes on, turn flasher out, ign off, turn signal center, right brake on, left brake off
Brakes on, turn flasher out, ign off, turn signal left, right brake on, left brake off
Brakes on, turn flasher out, ign off, turn signal right, right brake off, left brake on
Brakes on, turn flasher in, acc on, turn signal left, right brake on, left brake flash
Brakes on, turn flasher in, acc on, turn signal right, right brake flashing, left brake on
Brakes on, turn flasher in, acc on, turn signal center, right brake on, left brake off

Brakes off, hazards on, front signals flashing, right brake flashing, left brake off
Here's a weird one...
With the above conditions and then having the brake switch on, all flashing stops and the front turn signals go steady on, the right brake goes steady on and so does the left brake light. Weird!

Brakes off, hazards on, turn flasher out, turn signal left or right, both right and left brakes flashing.
Brakes off, hazards on, turn flasher out, turn signal center, right brake flashing, left brake off.

This one is a bit of a stumper but I leaning towards the turn signal switch being suspect. Any thoughts?

 

[NATEandALLI]

Reviewed my results and thought about this some more. So it would seem that the only time the left brake light works like it's supposed to is when the turn signal switch is either set to left or right. The left brake light never turns on if the turn signal switch is in the middle position. I guess that points towards the turn signal switch being the culprit.

Is having the brakes on and making the hazards stop flashing normal?

 

[NATEandALLI]

Is having the brakes on and making the hazards stop flashing normal?

Looked at the wiring diagrams more closely and I think this behavior is actually normal. The hazards switch basically ties together the front left and right turn signals and the 12v input to the turn signal for the brake lights and connects them to the hazards flashers as a pulsing on/off 12v power source. Having all these circuits tied together is what makes the brake and turn signals lights flash together when the hazards are on. When you press the brake, this also sends 12v to the hazard switch which has all those other circuits tied together so when the brake switch outputs a steady 12v, this "over rides" the hazards flasher that's plinking on and off and makes everything go steady on.

In all the years I've owned and worked on a multitude of old cars, I never encountered this before.

 

[NATEandALLI]

Wow, nobody?

 

[McLeod]

Is having the brakes on and making the hazards stop flashing normal?

Yes it is.

This probably won't be of any help but most early Ford trucks, when the brake lights are on and a turn signal activated, the flashing rear turn signal indicator will not display the brake light, it will only flash.

 

[SteveL]

Did everything work before you messed with the column?

 

[DirtDonk]

Yes, normal for any vehicle that uses the same filament for brake and turn signal/flasher. Can't really work any other way I don't think, but I suppose anything is possible.
Any vehicle with amber rear turn signals will continue to flash when the brakes are applied because it's a separate bulb completely independent of the brakes.

Dash indicators are always part of the front turn signal circuit only and not connected in any way to the rear turn signals/brake lights because you don't want the dash lights to come on every time you hit the brakes.
Any vehicle (that I know of anyway) where the turn signal indicators light up with the brakes, is simply wired incorrectly.

You did do a ton of testing and diagnosing NATEandALLI! It's a fun mystery, but I completely missed it yesterday. Now wishing Viper would have seen it. His powers of deduction when it comes to brake lights and turn signals are legendary.
Is that factory original wiring, or new Painless? Looks original (other than the connector of course) but figured I'd make sure.

When things are working in any way at the rear, are the brakes/signals bright and the running lights dim? Or does there seem to be any inconsistency there?
Are any of the lamp sockets, front or rear, new replacements?

Gonna have to think about it a bit more.

Paul

 

[gws34]

Try looking at your turn signal cam in the switch (in the steering column) I had a problem that took me a while to figure out and it was a problem with the internal turn signal switch.

It might be the same thing.

Glen

 

[Viperwolf1]

Turn signal switch is bad.

 

[NATEandALLI]

You did do a ton of testing and diagnosing NATEandALLI! It's a fun mystery, but I completely missed it yesterday. Now wishing Viper would have seen it. His powers of deduction when it comes to brake lights and turn signals are legendary.

Hi Paul, thank you for responding. Jumping ahead to Viper's response, it seems I have a bad turn signal switch but I'll answer your questions since you took the time to ask them.

Is that factory original wiring, or new Painless? Looks original (other than the connector of course) but figured I'd make sure.

Yes, original. Appears to be the original turn signal switch too.

When things are working in any way at the rear, are the brakes/signals bright and the running lights dim? Or does there seem to be any inconsistency there?
Are any of the lamp sockets, front or rear, new replacements?

I made sure to pay particular attention to this. I closely checked which filaments were on when doing my tests. When the brakes/signals the brighter filament lights up and is very bright. When the parking lights are on, the other dimmer filament is on. When things are on, they look normal. Nothing appears to be swapped or switched. Just that the left brake light doesn't work.

The sorta funny thing was that early on, only the left brake light worked. I found that the right brake light had 12v so must not have had a good ground so I added in a supplemental ground wire and that made it start working. I'm guessing that when the left brake light was working initially, it was probably because the turn signal wasn't centered which gave us a false positive.

 

[NATEandALLI]

Turn signal switch is bad.

Thanks for the reply. I'll get one on order asap!

 

[sprdv1]

Thanks for the reply. I'll get one on order asap!

And you thought no one was watching

 

[NATEandALLI]

Did everything work before you messed with the column?

Meant to answer this before. The Bronco showed up as a partially disassembled basket case. The engine ran (barely), was sorta driveable but had no brakes. Most the exterior electrical was disconnected and the tail lights were actually removed. So no, nothing really worked before. LOL.

We just put everything back together and kind of figured it out as we went. I'll be replacing the switch soon - I'm sure that'll probably take care of everything.

And you thought no one was watching

Well it did take a little poking but I knew I'd hear something eventually.

 

[NATEandALLI]

BTW for anyone reading this, I did a test where I bypassed the turn signal switch and tested just the brake switch. I did this in the body side of the turn signal switch plug under the dash by the steering column. I made a jumper that went from red/black (brake switch 12v) to yell/blk (left brake) and green (right brake). Doing this and pressing the brake pedal gets both brake lights to turn on nice and bright. This tells me that the wiring from the column back to the lights is good.

 

[DirtDonk]

Yep, that's a great test. Tells the tale right there.
Had time to get the new switch and install it yet?

Can't wait to hear the results.

Paul