'91 Brake Lights Always On

[rkgraves]

Thanks for your help!

Recently I noticed the brakes lights not working on our '91 4Runner (V6, SR5, 5 spd, cruise control). The 15 amp Stop Light fuse was blown, I replaced it, and the brake lights began working normally.

Later that day (towing and several hundred miles from home) same procedure; no brake light, blow fuse, replaced fuse, brake lights working OK again. As I was running out of fuses, the last fuse I installed was a 30 amp.

I have the vehicle home now and the brakes lights stay on continually. I have to pull the fuse in order to get them to turn off. I removed and tested the brake light switch and it is OK. Even with the brake light switch removed the brakes lights stay on constantly.

With the fuse installed I measure 12 vdc on both sides of the brake light switch. I believe I should only have 12 vdc on the fuse side of the switch.

I have the factory Electrical Wiring Diagram for our 4Runner and I can't see anything that would cause this symptom. The circuit looks straight forward and the only other device in the circuit is the Cruise Control Module. I've disconnected the cruise control module and the symptom remains the same. Even though the circuit is straight forward getting to the brake light wiring behind the dashboard is difficult.

I would appreciate any help, suggestions, or advice regarding.

Thank You,
Randy Graves
Coeur d'Alene, ID

 

[kdawg532]

Thanks for your help!

Recently I noticed the brakes lights not working on our '91 4Runner (V6, SR5, 5 spd, cruise control). The 15 amp Stop Light fuse was blown, I replaced it, and the brake lights began working normally.

Later that day (towing and several hundred miles from home) same procedure; no brake light, blow fuse, replaced fuse, brake lights working OK again. As I was running out of fuses, the last fuse I installed was a 30 amp.

I have the vehicle home now and the brakes lights stay on continually. I have to pull the fuse in order to get them to turn off. I removed and tested the brake light switch and it is OK. Even with the brake light switch removed the brakes lights stay on constantly.

With the fuse installed I measure 12 vdc on both sides of the brake light switch. I believe I should only have 12 vdc on the fuse side of the switch.

I have the factory Electrical Wiring Diagram for our 4Runner and I can't see anything that would cause this symptom. The circuit looks straight forward and the only other device in the circuit is the Cruise Control Module. I've disconnected the cruise control module and the symptom remains the same. Even though the circuit is straight forward getting to the brake light wiring behind the dashboard is difficult.

I would appreciate any help, suggestions, or advice regarding.

Thank You,
Randy Graves
Coeur d'Alene, ID

I'm not an expert on these things, but I think the 30amp fuse may be allowing to much amperage to be running through the wires causing the relay/switch to get stuck on.

 

[rkgraves]

Thank you for your reply!

I agree that adding a 30 amp fuse was not the best idea. I was several hundred miles away from home and had run out of 15 & 20 amp fuses. I did remove the Brake/Cruise Control switch and tested it with a VOM meter and the switch tested good. (normally-open contacts for brake and normally-closed for cruise control). Also, the brake lights stay on even with the brake light switch removed. I must remove the fuse in order to get the brake lights to go out.

I work at a Community College and talked with our auto shop instructors. They suggested I remove any trailer wiring harness, as they were concerned that a diode in the 3-to-2 wiring box could have gone bad. I removed the trailer wiring, and while a good idea, it did not change the symptom.

My next thought is to disconnect the connectors between the front and rear of the vehicle and see if I can isolate where the 12 vdc is coming from. It is a pretty simple circuit, but the wiring under the dash is hard to get too.

I am hoping someone has seen this before.

Thanks for any input anyone can offer!

Randy Graves

 

[rkgraves]

Just wanted to update my original post. Thanks for reading it!

My only thought is that maybe someone has seen this problem before and can point me in the right direction.

The brakes lights always-on symptom is now intermitent. Went 2 weeks without the problem and then it showed up again yesterday. When I parked I noticed the brakes lights on and pulled the fuse while away, so as to not run the battery down.

When I returned I reinserted the fuse (noticed a pretty big spark) and the light were out. They have been working correctly since.

I'm going to wire back in the trailer harness today as I need to tow later later this week.

Thanks for any help or input regarding!
I appreciate it!

Randy Graves