Third Brake Light Electrical Issue

[FloridaCruiser22]

The third brake light on my 80 has been out for...........3 years now. I decided to try to diagnose it a month ago and was stumped, so now I'm here a month later. Procrastination

This is what I've checked so far and I am confused about which direction to go next -

- With the key off --> third brake light comes on
- Pressed the brake pedal --> connector is receiving 9 volts
- With the key on --> third brake light is off
- Pressed the brake pedal --> connector is receiving 3 volts
- Checked the ground wires to the taillights and they look fine

The only thing I can think of is there's a hidden wiring issue/breakage that I'll have to trace backwards. Any suggestions or someone who's dealt with something similar?

 

[Kernal]

@jonheld might know

FWIW some links that might help:

K

Thread 'Third Brake Light Not Working on 1996'

Feb 29, 2012

My third brake light is not working right now. When I went in for vehicle inspection today, I failed because my brake light was not working. When I checked it, it was working again. I just checked and it is not working, again. What gives? I did a search but no one tells how to actually fix the problem.

Can anyone give me instructions on what to do to get this working again so I can get this REJECTION sticker off my truck? Thanks!

• kino1161
• Replies: 52
• Forum: 80-Series Tech

Thread 'Third Brake Light troubleshooting/rebuild tips'

May 30, 2021

If your 3rd brake light is not working, working poorly, or half working. Only a few pics and assuming basic familiarity with soldering, soldering irons, and heat. And this is just the tools and methods I used to address the situation on my hands: light was working but it was very dim and half the LED's wouldn't light up.

Shoutout to the MUD member posting this link (can't find it again) DIY Landcruiser Third Brake Light Fix: $0.69 - http://the36thlock.blogspot.com/2010/08/diy-landcruiser-third-brake-light-fix.html. I went with their zener diode voltage - 5.1V They say if the...

• LandLocked93
• 3rd
• Replies: 2
• Forum: 80-Series Tech

• 

 

[FloridaCruiser22]

Search is your friend

Not an electron guru but assuming you don't have a broken wire going to the third brake lamp, search this forum for ZENER DIODE

(Did it for you)

K

Thread 'Third Brake Light Not Working on 1996'

Feb 29, 2012

My third brake light is not working right now. When I went in for vehicle inspection today, I failed because my brake light was not working. When I checked it, it was working again. I just checked and it is not working, again. What gives? I did a search but no one tells how to actually fix the problem.

Can anyone give me instructions on what to do to get this working again so I can get this REJECTION sticker off my truck? Thanks!

• kino1161
• Replies: 52
• Forum: 80-Series Tech

Thread 'Third Brake Light troubleshooting/rebuild tips'

May 30, 2021

If your 3rd brake light is not working, working poorly, or half working. Only a few pics and assuming basic familiarity with soldering, soldering irons, and heat. And this is just the tools and methods I used to address the situation on my hands: light was working but it was very dim and half the LED's wouldn't light up.

Shoutout to the MUD member posting this link (can't find it again) DIY Landcruiser Third Brake Light Fix: $0.69 - http://the36thlock.blogspot.com/2010/08/diy-landcruiser-third-brake-light-fix.html. I went with their zener diode voltage - 5.1V They say if the...

• LandLocked93
• 3rd
• Replies: 2
• Forum: 80-Series Tech

• 

I've looked it up previously and have seen zener diodes mentioned but I think it working with the key off was throwing me for a loop.

I went ahead and ordered a pack of them and will give that a shot and report back!

 

[FloridaCruiser22]

Well update - replaced the zener diode and still have the same issue. I guess I'll be tracing wires

 

[thedoughboy]

@FloridaCruiser22
Do you have LED rear tail lights with resistors installed?

 

[FloridaCruiser22]

@FloridaCruiser22
Do you have LED rear tail lights with resistors installed?

I have LED reverse lights and then the brake lights are just standard sylvania bulbs

 

[97 80 LC]

I went through this earlier this year, also my rear wiper didn't work either. Both the wiper motor and brake light assembly worked properly when disconnected / isolated and tested separately. Started troubleshooting by reworking the grounds under the center console and under the rear near the spare tire, as discussed. Also cleaned and greased the connectors on the hatch, rear drivers quarter panel area and rear drivers headliner. This solved the rear wiper not working. But the brake light would only light up a little, very dim, when pressing on the brakes.

Measured voltage with a digital meter at the rear brake light connector in the upper hatch next to the brake light assembly, and got +2V at the ground side from a known good ground and +12V on the high side. I figured it had a bad ground so I temporarily attached a wire from the ground side of the connector to the bare metal at the light mounting bolt, and it worked properly! Ended up splicing in a new wire onto the old ground wire and adding a connecter to the bolt where the light mounts. Maybe give it a try with a short temporary wire and see if that solves it.