brake lights killing me

[datinmayne]

ok ive tried everything brake lights not working, third not working and hard to shift in and out of gear. the tail lights, turn signals, hazzards and reverse lights work. ive checked the tail lights and all the fuses i changed the switch on the pedal and ive had 2 different turn signal switches in it and still nothing. its driving me crazy i think i just got a bad turn signal switch i did get it from a junk yard and every once in awhile they work when first started and as soon as i drive more than 400 ft they stop again but i cant even get them to do that any more

 

[ak diesel driver]

I'd try new circuit boards in the taillight assembly.

 

[THEFERMANATOR]

The third brake light doesn't go through the turn signal switch and isn't affected by the bad rear tail light boards. Also the brake switch is 3 switches in one, brake lights, nuetral safety portion to release the shift interlock, and the ECM brake feed for the torque converter lockup. With all 3 sides having problems, you need to look long and hard at the brake light switch and it's wiring as it is the only area all 3 groups tie together at.

 

[datinmayne]

Sorry I have been on in awhile got busy with a lot of other projects but I have gone through all the wiring and the switch with a fine tooth comb and still not turning up any problems I did just check the third brake light and the bulbs are burn so I think I will go tomorrow and get bulbs and if that works for them I don't know where to go from there

 

[handcannon]

The third brake light doesn't go through the turn signal switch and isn't affected by the bad rear tail light boards. Also the brake switch is 3 switches in one, brake lights, nuetral safety portion to release the shift interlock, and the ECM brake feed for the torque converter lockup. With all 3 sides having problems, you need to look long and hard at the brake light switch and it's wiring as it is the only area all 3 groups tie together at.

This is not directly on topic, but, it may involve the brake switch.

This involves a 94 K2500 pickup.

A few days ago I was on the freeway, and was using the cruise control. I exited and stepped on the brake pedal to slow down. I couldn't slow down! I pressed harder on the pedal. The tranny downshifted, motor reved up, but continued to try to maintain speed. Then the speed suddenly started to drop, as it should have at the first. My first thought was tranny, but after spending time thinking it through I've come to the conclusion that the cruise did not drop out like it should have when I stepped on the brake pedal. That evening I tried the same scenario. The exact same thing happened. I haven't had a chance to use the CC since.

My question is, does this same switch shut off the cruise control when you step on the brake pedal? If so, I may also have problems with the brake lights.

Don

 

[WarWagon]

Can be related to cruise not kicking off. Cruise WILL kick off if you drop ~16 MPH below the set point so you may have triggered this safety cut out. Don't forget you can use the cruise switch to turn it off. Back up to a building window and you can tell if the brake lights are working from a reflection.

 

[handcannon]

Thanks WW for the reply. Just now got back to this, been a very busy week for me. I haven't been driving my pickup very much for the past year or so, my Astro gets a bit better fuel mileage. But, I had to drive it today. I forgot about the CC problem and was caught by surprise again today.

I think that the safety cut out you referenced is what has been turning the CC off. It fits the symptoms, and what has been happening. I did end up using the off switch while doing some more testing.

I just went outside to check for brake lights, pitch black, clouded over, no moon/stars, no houses close so no light there. It was interesting to go from a well lit house to a dark driveway and trying to find my way while my eyes adjusted to the lack of light, and I forgot my flashlight. No light when I stepped on the brake pedal. So now, as soon as I have the time I need to check fuses and brake switch.

Don

 

[handcannon]

I have been busy and have not re-visited my brake light problem until this week. To recap-- no brake lights, cruise won't shut off with the brake pedal, and four way flashers do not work. Tail lights work, turn signals work, back up lights work, I have power at the brake fuse , fuse is good. My pickup is a 94 K2500, as shown in my post signature.

I have a diagnostic chart - exterior lights, for a 95, but there was a major wiring change under hood between the 94 and 95 models so I don't know if the chart is viable. The "95" chart states with the symptoms stated above to "Locate and repair open in ORN (140) wire between fuse block and splice S251". I do not have any power at the ORN wire in the brake switch connecto r. I do not know if this path is viable for a 94 so I am going to go to local library and see if I can find a brake light/cruise control wiring chart. If I am not able to find a chart does anybody on here have one? I need to trace this down.

I am questioning if the turn signal switch in the column is in the mix and also need to know about wiring between the brake light switch and the turn signal switch.

Don

 

[Will L.]

Brake light switch is like $10. It is the only connecting point as Ferm mentioned, and is the only wear point besides a short. Easy to change, just not a cozy body position for a nap. Yes the brake light switch is were the "signal" comes from to kick out cruise control. We stocked them in our parts room for the fleets, well known wear problem. Although I always warn against throwing in a part without diagnosing it, that is how I would do it in this situation. If it turns out to not be it, hold on to the switch you will need it in a few more years.

 

[handcannon]

Thanks for the reply Will. What you said in your post is exactly what I did. I had to order some other stuff from Rockauto so I just included a new AC Delco switch for about $8. It didn't work. I'm far from financially able to just replace stuff willy-nilly. The wife was off work for two months this fall and we are still struggling to keep our heads above water with all the unexpected Dr bills. Her pay check is extremely important to us.

This is the second time I've had to remove that pesky clip that holds the brake switch onto the pedal pin. This time I removed the seat. So much easier on this old abused back as I could lay flat on my back, not in a pretzel position. This time I had the clip off in less than five minutes. I could just barely see the switch, or the clip, but not both at the same time.

In my stash of stuff I copied off the net I had a diagnostic list for a 95 K2500, mine is a 94, and it said to check the orange wire at the switch. If no power then try the four way flashers. If they don't operate then "Locate and repair open in orange wire (140) between fuse block and splice S251". I have no power on the orange wire at the switch, and the four way flashers don't work.

I had started to post this question yesterday morning, but a senior moment must have happened and I found this question still unposted this morning. I did get to the local library yesterday afternoon. The wiring schematic I found online on their system showed that there is not anything between the brake switch and the fusible link EXCEPT for the splice where the power to the ignition switch takes off, and the fuse. The schematic shows that there are two Ign wires coming from that splice and go to connectors C255 and C256, both going into the Ign switch. I can't think of anything connected to the Ign switch that is not working.

The schematic shows red wire from fusible link to splice to Ign Sw, then red to fuse block, through fuse, then orange to brake switch. When I tested the fuse it appeared to be switched power, which I questioned, but didn't follow up on. The schematic shows that circuit to the fuse as unswitched. So I'm going to have to re-test that, and maybe pull the fuse block out and check the back side. After the fuse the brake light switch (doesn't work), hazard flasher (doesn't work), rear wheel anti-lock brake relay (don't remember idiot light on dash being on), audio alarm module convenience center (my buzzer has been working unreliably lately).

Sorry for all the rambling, but this is helping me think this through.
1) double check the brake fuse, should be unswitched, if power----
2) check the back side of the fuse block, schematic shows the four items noted in the previous paragraph spliced after the fuse, is the splice at the fuse block or after? does power go through to the back side of the block how does it leave from there? at least two of the four items here are not working

If ANYBODY has any ideas, especially of where under the dash to look for these items PLEASE speak up.

Don

 

[THEFERMANATOR]

If you have no power at the orange wire, check at the fuse panel and see if the stop fuse has power to it. From what i can find it should be a 15 amp fuse in the fuse panel inside the truck.

 

[handcannon]

Thanks Ferm for the reply. I have checked that fuse, and it has power to it, and through it. The one strange thing I have found is that according to the wiring schematic, and according to all I have been used to, that fuse should have unswitched power. But, it is definitely switched power. I just got through double checking it. My test light is in the fuse socket, the light goes on when the switch is turned on, and goes off when the switch is turned off.

I have other things to do first, but as soon as I have time I intend to figure out how to remove the fuse panel and check the back side.

Don

 

[Will L.]

What switch, ign? If it should be unswitched, but is only getting power when keyed up, then it could be getting back fed, and the proper power supply is an open circuit, which could be your problem.

 

[THEFERMANATOR]

What switch, ign? If it should be unswitched, but is only getting power when keyed up, then it could be getting back fed, and the proper power supply is an open circuit, which could be your problem.

What he said. It sure sounds like somebody has cross wired soemthing under the dash, or your backfeeding power. The brake lights fuse should DEFINATELY NOT be keyed but hot al lthe time since it is also the power for the hazard flashers(which are DOT mandated to be powered directly from the battery).

 

[handcannon]

Well, I feel kind of stupid now. I spent a lot of time tracing out stuff and scratching my head wondering why I had only keyed power to the brake fuse. I left the pickup setting today and went to work on cleaning up brush and moving wood from a tree I had cut down. My back started to bother me after a while, so I went inside and sat down.

I picked up the notebook I have all my schematics for the pickup in to puzzle over the problem again. It suddenly hit me, not all the fuse block was shown on the one page. I flipped a page and there it was, a second fuse which was labeled brake fuse. The fuse I had been looking at on the schematic was labeled stop/hazard. The fuse I had been working with in the pickup was labeled brake.

According to the schematic the brake fuse is for the vehicle speed sensor and anti-lock brake module, and is keyed hot. This is the one I've been frustrated with, and it was the wrong fuse. The stop fuse in the pickup is hot all the time, as it should be, and was blown. When I pulled that fuse one of the blades stayed in the fuse block. It was not blown in a way that I'm used to, burned apart in the center of the element. The element was gone starting from the center and completely over to the blade that pulled out of the fuse body, and the attaching point on the blade showed that where the element had been attached had gotten hot.

For the past few months the buzzer under the dash had not been operating all the time. It would work, sometimes for just a few seconds, sometimes longer. Then when the brake lights quit working I noticed the buzzer no longer worked. As soon as I installed a new fuse the buzzer started working again. I'm guessing the stop fuse has been defective for a while, the one blade may have been loose in the body and the element may have not been fully attached. That weak spot finally got hot enough to blow. This is just pure speculation, but my best guess at this time.

I WILL be watching this close for a while just to make sure there is nothing causing the fuse to blow.

Thanks Will and Ferm for your help.

Don