no brake lights

[Russ 71Mach1 07GTCS 16GTCS]

Ive replaced every switch. Steering column, brake pedal and ignition switches. all other lights work. what is left to check/replace?

 

[Sheriff41]

Did you check the wires for continuity?

 

[72conv]

Looking at the schematic now. Do the emergency (4-way) flashers work?

EDIT: The reason I'm asking is that there is a circuit breaker in the power feed to the brake light circuit, and it also feeds the emergency flasher circuit. If yours has failed, you'll have no power to the brake lights or emergency flashers. This breaker is located on the breaker panel above the glove compartment.

My car is a convertible with power windows. DC power to the top motor and power window circuits is fed through one circuit breaker. A while back my top and windows both stopped working. The circuit breaker had failed open. I got a replacement at O'Reilly's for a few bucks.

 

[Tnfastbk]

Also make sure you have the right bulbs installed. If you have tail lights and just no brake lights. Never know..........

 

[Fabrice]

Aside the basic circuit, if you have replaced the brake booster, keep in mind not every rod is equal.
I had a problem (no brake lights) after replacing mine and fixed the problem as on the pict;
I bet the same can occur if you've only replaced the switch.

https://cdn.imagearchive.com/7173mu...0025ebc84045adacf68d64cbcb1cfdc92aea6fc01d5cb

 

[giantpune]

Did you check for 12v at the brake light socket when somebody presses the pedal?
And +1 for having the correct bulbs with the right number of conductors.

 

[72mokk1]

Ive replaced every switch. Steering column, brake pedal and ignition switches. all other lights work. what is left to check/replace?

I would do what giantpune said first otherwise I am looking at circuit 14 from the taillight to connector C44 left hand cowl under the instrument panel. Check for a good clean connection, I use copper and brass cleaner to clean them. The wife's eyelash brush fits inside the female connector pretty well. Don't forget to clean off the cleaner with water and dry them. A dab of Dielectric grease will help against corrosion.
I trouble shot the hell out of my back blinkers until I realized the front bulbs were not in...it's the simple things.

 

[72mokk1]

Looking at the schematic now. Do the emergency (4-way) flashers work?

EDIT: The reason I'm asking is that there is a circuit breaker in the power feed to the brake light circuit, and it also feeds the emergency flasher circuit. If yours has failed, you'll have no power to the brake lights or emergency flashers. This breaker is located on the breaker panel above the glove compartment.

My car is a convertible with power windows. DC power to the top motor and power window circuits is fed through one circuit breaker. A while back my top and windows both stopped working. The circuit breaker had failed open. I got a replacement at O'Reilly's for a few bucks.

Good call on checking the circuit breaker.

 

[Boss351 45yrs & Counting]

Ive replaced every switch. Steering column, brake pedal and ignition switches. all other lights work. what is left to check/replace?

I personally had this issue for many summers as I only drive our Boss 351 in the summer. I did everything as it sounds you have. I actually finally found the issue to be in the multi pin connector that is on the steering column. just above the brake pedal. When I separated it and viewed both the male and female pins I noticed 1 pin that was slightly lower than all rest and darn if it wasn't the Brake light wire. I was able to push the female up slightly and presto brake lights. As crazy as it might sound my theory is that it was in the that lower position since assembly. But as a daily driver the 12volt current made that little jump from that slight space in connectors. But since only driving it occasionally over 20 years a slight corrosion prevented the current to make the jump. So for 10 or more summers that issue was present. Since the fix approx 8 summers ago I have brake lights always. Good Luck maybe my experience will get your lights working. Dave

 

[rcadd1ct]

Also check you have good grounds at the rear light harness

 

[mrgmhale]

The suggestion to check the circuit breaker is a good one, assuming you have no voltage to the switch. But, there is another item (or two) you should look at. I had a car come in with a no brake light situation. He had taken the car to several other shops, but even with new bulbs and a new brake light switch, his brake lights were not working. But, all the 4 way flasher bulbss would work! I began to poke around with my test light, I one I used has a plastic hook design that allows me to pull a trigger and have the test electrode (needle) pierce the insulation to test for current being present. Here is a link so you can see the design:

https://www.usafleetsupply.com/proddetail.asp?prod=Redline+Quickee+Wire+Circuit+Tester+for+6V+12V+Systems&gad_source=1&gclid=Cj0KCQjwztOwBhD7ARIsAPDKnkDgHpjMb_UjL4VQh8_AO4AQBATStRJlshkH5gFKiYcKwaH-ol5jnlEaAkdwEALw_wcB

The reason I used the hook style tester is because I wanted to test for voltage traveling through the wires with the new style tester (I had just purchased it). I then used my conventional tester to check the metal terminals locked inside the brake light switch connector. I found that Circuit #10 (Light Green & Red Hash Mark wire) was carrying a current, but the metal terminal locked inside the brake light switch had no current. It turns out the stranded wire inside the insulation had fractured near the brake light switch, but the sire insulation looked fine, no breaks, no cracks, no thin spot in the insulation sheath, nothing that made it look like there was a problem inside the wire itself. I had never see anything like that before (I was fairly new in the auto repair game at the time, 1978 or so). The only reason why I decided to use both test light styles was because the hook style tester was new and I wanted to start using it. Dumb ass luck, eh?

Anyway, If you are not getting current at the Circuit #10 metal terminal that is locked in the brake light switch connector I suggest checking the wire leading to the switch connector. If the wire for circuit #10 also has no power it is time to check the power at the circuit breaker above the glove box. Below is a link to my Google Drve where you will find some PDF files that have various info on the brake light circuit for 1973 Mustangs (I am pretty sure the wiring is the same for 71-72 Mustangs), to include a photo of the circuit breaker for the brake light switch, and lots of schematics and related info. There is a lot of overlapping info in the files. I suggest you take the time to look at each of the three files.

https://drive.google.com/drive/folders/11Dfd0BZkKF5uq129bXa2eFIVHxRwtO8t?usp=drive_link

If you find the cause of the problem I hope you will share your findings in this thread. I am really curious...

 

[Russ 71Mach1 07GTCS 16GTCS]

The suggestion to check the circuit breaker is a good one, assuming you have no voltage to the switch. But, there is another item (or two) you should look at. I had a car come in with a no brake light situation. He had taken the car to several other shops, but even with new bulbs and a new brake light switch, his brake lights were not working. But, all the 4 way flasher bulbss would work! I began to poke around with my test light, I one I used has a plastic hook design that allows me to pull a trigger and have the test electrode (needle) pierce the insulation to test for current being present. Here is a link so you can see the design:

https://www.usafleetsupply.com/proddetail.asp?prod=Redline+Quickee+Wire+Circuit+Tester+for+6V+12V+Systems&gad_source=1&gclid=Cj0KCQjwztOwBhD7ARIsAPDKnkDgHpjMb_UjL4VQh8_AO4AQBATStRJlshkH5gFKiYcKwaH-ol5jnlEaAkdwEALw_wcB

The reason I used the hook style tester is because I wanted to test for voltage traveling through the wires with the new style tester (I had just purchased it). I then used my conventional tester to check the metal terminals locked inside the brake light switch connector. I found that Circuit #10 (Light Green & Red Hash Mark wire) was carrying a current, but the metal terminal locked inside the brake light switch had no current. It turns out the stranded wire inside the insulation had fractured near the brake light switch, but the sire insulation looked fine, no breaks, no cracks, no thin spot in the insulation sheath, nothing that made it look like there was a problem inside the wire itself. I had never see anything like that before (I was fairly new in the auto repair game at the time, 1978 or so). The only reason why I decided to use both test light styles was because the hook style tester was new and I wanted to start using it. Dumb ass luck, eh?

Anyway, If you are not getting current at the Circuit #10 metal terminal that is locked in the brake light switch connector I suggest checking the wire leading to the switch connector. If the wire for circuit #10 also has no power it is time to check the power at the circuit breaker above the glove box. Below is a link to my Google Drve where you will find some PDF files that have various info on the brake light circuit for 1973 Mustangs (I am pretty sure the wiring is the same for 71-72 Mustangs), to include a photo of the circuit breaker for the brake light switch, and lots of schematics and related info. There is a lot of overlapping info in the files. I suggest you take the time to look at each of the three files.

https://drive.google.com/drive/folders/11Dfd0BZkKF5uq129bXa2eFIVHxRwtO8t?usp=drive_link

If you find the cause of the problem I hope you will share your findings in this thread. I am really curious...

Gents- thanks 4 all the ideas. I will let u know what I find out. Getting busy again now an won't get to until we have a rainy day. Grateful for all the support