Brake light troubleshooting help

[toddz69]

A few weeks ago, a fellow motorist rolled down their window while we were sitting in rush hour traffic and told me I didn't have any brake lights. Wha???

So I stopped and checked them and sure enough, no brake lights. So I've been doing some checking and apparently when my vehicle is 'cool', I have brake lights. They work all the time when it's parked in the garage and they were working when I backed it out of the garage last night and drove down the street. I drove it about 1/4 mile last night before they stopped working.

Turn signals and tail lights work at all times. I have power on both sides of the brake light switch whether the brake lights are working or not. Last night I checked my hazards when the brake lights weren't working and it appeared that I only had hazards (f/r) on the right side of the truck. Soon thereafter I started the truck again and the brake lights and hazards started working properly again. It appears they start working again once the truck cools down.

A quick look at the wiring diagrams doesn't give an obvious clue as to why the hazards not working correctly would correlate to the brake light issue.

Seems like I might have a bad connection somewhere around the light switch? that opens up with just a little bit of running time on the truck.

Any thoughts?

Thanks,
Todd Z.

 

[Viperwolf1]

I wouldn't think the hazard switch would cause any problems. The hazard switch just connects the two front lights and brake lights together along with it's own power through a flasher. The brake lights are on a single wire at the hazard switch so the problem has to be after that switch, which points to the turn signal switch. That is where your problem lies.

 

[tk1218]

Is your hazard on the dash or on the steering column?

 

[surfer-b]

brake light pwr goes through the turn sig switch as Viper stated, it has to because the brake light filiment is the same as the turn, so if turn sig is applied the brake light on that side will not make connection, I bet its in the turn sig switch

 

[toddz69]

Is your hazard on the dash or on the steering column?

It's on the dash.

Todd Z.

 

[toddz69]

I wouldn't think the hazard switch would cause any problems. The hazard switch just connects the two front lights and brake lights together along with it's own power through a flasher. The brake lights are on a single wire at the hazard switch so the problem has to be after that switch, which points to the turn signal switch. That is where your problem lies.

Thanks Viper - I'll take a look at it.

Todd Z.

 

[toddz69]

brake light pwr goes through the turn sig switch as Viper stated, it has to because the brake light filiment is the same as the turn, so if turn sig is applied the brake light on that side will not make connection, I bet its in the turn sig switch

Thanks - I'll be taking a look at it.

I also should note I have a Flaming River column so I should probably look at the wiring going into the column at some of the adapters too.

Todd Z.

 

[garberz]

A while ago I had a small amount of electrical smoke come out of the column, which later I realized one brake light was not functioning anymore. Everything else was working properly. I was just about to research who was a good supplier of turn signal switches, when it magically fixed itself.

Mark

 

[ngsd]

The intermittent part is the puzzler. It could be coincidental that there is a loose wire or short that just happens when driving not cold or hot but tracing that one is fun. The color coding I assume was right before you had an issue so I doubt that is wrong but perhaps it has been doing it for awhile and you never knew it either? Not knowing what year it is the matching of wires would be a good start I assume?

 

[toddz69]

The intermittent part is the puzzler. It could be coincidental that there is a loose wire or short that just happens when driving not cold or hot but tracing that one is fun. The color coding I assume was right before you had an issue so I doubt that is wrong but perhaps it has been doing it for awhile and you never knew it either? Not knowing what year it is the matching of wires would be a good start I assume?

I'll have to look closely at the wire colors - Viper mentioned a red wire above and I think the wire coming off the 'activated' tab on my brake switch is red but I don't know that for sure. My truck is a '69.

I'm guessing it's been doing it for awhile and I didn't realize it.

Todd Z.

 

[Viperwolf1]

The power wire going into the brake light switch is red. The wire going from the brake light switch to the turn signal switch and hazard switch is red-black.

 

[toddz69]

The power wire going into the brake light switch is red. The wire going from the brake light switch to the turn signal switch and hazard switch is red-black.

Thanks Viper - maybe I'll have a chance to look closer tonight with a good light before it gets dark. I'm guessing some of my wire colors have been changed there due to some 'rework' in that area over the years.

To confirm - constant hot power should come in at the lower tab on the switch and switched power goes out through the upper tab, correct?

Thanks,
Todd

 

[DirtDonk]

You can also check another function while you're at it (and also to delay digging into the switch or getting under the dash!) by pressing the brake pedal while the other stuff is supposedly working.

If you press the brake pedal with the hazard flashers working, they should stop and stay steadily lit. At this point you know that the brake light switch is working for sure. I know you tested it's output and found it good, but with intermittent stuff you can't do too many tests.

Like the others have said though, it sure seems like something with the turn signal switch.
If original wiring though, do the brake and tail light wires pass through the two firewall connectors? Or do they have their own pass-through location in the firewall? If part of the two connectors, you could hunt there for an intermittent issue from possible corrosion.
Unless yours are falling apart, it's not a bad idea to pull them apart every couple of years to clean them up. And maybe even to add some dielectric grease while you're at it if you haven't already.

You might be in AZ, but I don't think that renders your '70 and earlier Bronco immune to the gremlins associated with those two connectors.
Even if they have nothing to do with your issue then, it's not a bad idea to check them out.

Paul

 

[Broncobowsher]

Todd,

Check the wires at the brake switch. I have done several Fords over the the years where the wires fatigue and break as they go to the brake switch. Usually where the wire is crimped to the brake switch connector but have seen it in the wire as well. It isn't a lot of movement, but it happens over a long enough time.

 

[Viperwolf1]

To confirm - constant hot power should come in at the lower tab on the switch and switched power goes out through the upper tab, correct?

I'd like to confirm that but I can't. Of the 5 EBs on the property here, none have stock brake switch connectors.

 

[ngsd]

These have helped me every time. I am sure you have this but the link is attached in case you are searching.

https://seabiscuit68.tripod.com/images/68-69exterior-color.gif

 

[Madgyver]

Check your grounds. heat expands metal making greater contact. just a thought.

 

[toddz69]

You can also check another function while you're at it (and also to delay digging into the switch or getting under the dash!) by pressing the brake pedal while the other stuff is supposedly working.

If you press the brake pedal with the hazard flashers working, they should stop and stay steadily lit. At this point you know that the brake light switch is working for sure. I know you tested it's output and found it good, but with intermittent stuff you can't do too many tests.

Paul

Paul - I did this test and got it to check out just like you describe.

Thanks,

Todd Z.

 

[toddz69]

Todd,

Check the wires at the brake switch. I have done several Fords over the the years where the wires fatigue and break as they go to the brake switch. Usually where the wire is crimped to the brake switch connector but have seen it in the wire as well. It isn't a lot of movement, but it happens over a long enough time.

Thanks Tim - I have two spade connectors that attach to the switch terminals - the original plug (I think there was one with both wires attached?) is gone.

But I think you're onto something. I did some repair work down there a few months back and installed new spade connectors and cleaned up the wiring, I thought, at the same time. Tonight I was able to get the brake lights to randomly quit working when I did some inadvertent fiddling with the wires/switch at some point. I think I did it twice. But I don't know what I did to make it fail! And then I'm not sure what I did to make it work again!

The first thing I'm going to do is get some pedal bushings back in the assembly so the switch assembly doesn't flop around so much. It seems like the switch randomly moving around a bit makes things work/not work?

Todd Z.

 

[Rustytruck]

the only time I had trouble with the brake lights was with the brake light switch its self. where the flat part of the Brake rod turns into the brake light switch the metal of the switch which contacts the Brake rod flat was collapsing. this altered the contact set point of the switch. I had to replace the switch. then all was well again.