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Old 04-29-2017, 11:40 PM   #1
GMC86
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Default Flashers show hazards
I have a 1986 GMC K1500 with a 305 engine. I've been trying to track down an issue with my brake lights. I got pulled over for no brake lights the other day. I tore the tail light assembly apart and replaced the bulb. My running lights worked but my brake light on the driver side did not work. Replacing the bulb had no affect. I then checked the ground behind the assembly it was rusted and corroded so I cleaned that up and reinstalled it. Everything worked flawlessly at that point so I drove into town and picked up some stuff and on my way home my wife was following me and said that when I was blinking my lights indicated hazards even though the hazard switch was not pulled. She said that when I would press the brakes while blinking the blinkers would work properly (without hazards) only to return to indicating hazards once I released the brake pedal. Also neither my brake lights or running lights are working now. We checked all the fuses and all were working according to our test light. About two weeks before all this started we did tear up the steering column to replace a part for the ignition. That required removing the hazard switch. Also my gauge light has always been very dim. This might be unrelated but I know that ties into the light switch behind the light plunger. Sorry if that's too much information. What do you think could cause the lights to indicate hazards instead of blinking? Also no brake lights?

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Old 04-30-2017, 01:21 AM   #2
 
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I'm going to go with turn signal switch, they are very well known to cause a lot of problems.


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Old 04-30-2017, 01:33 AM   #3
 
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Originally Posted by RetroC10Sport View Post
I'm going to go with turn signal switch, they are very well known to cause a lot of problems.
That's what I'm thinking. The turn signal and hazard switch are integrated. If you were in the column, it's possible you bent one of those metal tangs to that switch. They're fairly fragile once they get aged and brittle.


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Old 04-30-2017, 12:14 PM   #4
 
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I have experienced the same problem. Recently my drivers side brake light intermittently works, then doesn't work. I checked the ground connections, bulbs work, traced power from the fuse panel to the tail light clusters. Sometimes the brake lights work...sometimes they don't. Now it seems that the passenger side brake light is the one which won't illuminate.

So far I have replaced the brake light switch at the brake pedal bracket with the same results...



I was looking into a bad hazzard light switch/plunger mechanism.

Thanks to you post, I think that I too will have to tackle the turn signal switch to see if that is the problem. Please post your results and or findings. I have been troubleshooting this issue for weeks and certainly feel your frustration.


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Old 04-30-2017, 02:16 PM   #5
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Default I'll try that
when we were in the steering column we did replace the springs on the turn signal switch as one was broken and the switch would not return automatically when indicating a left turn. I might have to dive back into that and try replacing the whole switch. That could make sense. I've noticed a very slow blink at times and I wonder if that switch isn't fully engaging. I'll try that and return with my findings. I'm also going to double check that ground behind the tail light assembly to make sure it's not coming loose. I did see some dsmaged wires that run to the battery today as well. Some had corrosion. Could it possibly still be a grounding issue?
@Smoothandlow I've been following your thread as well in hopes that maybe you had already figured it out too lol. I guess we are stuck in the same boat till we figure this one out.
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Old 05-01-2017, 10:03 PM   #6
 
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Well....two minds are better than one. I hope that I don't have to tear down my steering column in order to replace the turn signal switch. By the looks of it, getting to the switch is a major pita.


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Old 05-09-2017, 10:20 AM   #7
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Originally Posted by smoothandlow84 View Post
Well....two minds are better than one. I hope that I don't have to tear down my steering column in order to replace the turn signal switch. By the looks of it, getting to the switch is a major pita.

getting to the switch isn't that bad. there is a bunch on stuff to come off, but the real pain is getting the new connector down to the bottom of the column
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Old 05-11-2017, 04:56 PM   #8
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Default Turn indicator switch didn't work
So I finally got in there and replaced it. You were right about the column tear down. It's not too bad until you have to run the wire through the column and then it's a pain but I replaced it with a new switch and it's still having the same issue. No change. To recap the issue at hand, using both left or right blinkers will show hazards being flashed on all four exterior lights. In the cab when I blink the correct blinker is showing. However the hazards are blinking very dimly, also the tailights and the brake lights are very dim.
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Old 05-18-2017, 11:41 PM   #9
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Default Any suggestions?
A friend of mine suggested to try replacing the flasher relay to see if that Is the problem. I wasn't very sure if that would make sense. What do you guys think?
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Old 05-19-2017, 02:26 AM   #10
 
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Originally Posted by GMC86 View Post
A friend of mine suggested to try replacing the flasher relay to see if that Is the problem. I wasn't very sure if that would make sense. What do you guys think?
As a test, you can just switch the hazard flasher with the T/S flasher. If it works buy a new T/S flasher.

But, I can almost 100% guarantee you - that won't solve your problem.

If I had to venture a WAG, I would say that you have a cross connection between the LH & RH directional lamp feeds. When either side is selected, power is then supplied to both sides of the circuit (L/R & front/rear). Since both the hazards and the blinkers use the same filaments in each lamp, all of them start blinking. This gives the appearance of the hazards being operated.

I would start at the light assemblies themselves. Be sure that each socket has the correct lamp installed (1157) and that it is properly fitted into the socket.
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Old 05-19-2017, 11:35 AM   #11
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Originally Posted by GMC86 View Post
So I finally got in there and replaced it. You were right about the column tear down. It's not too bad until you have to run the wire through the column and then it's a pain but I replaced it with a new switch and it's still having the same issue. No change. To recap the issue at hand, using both left or right blinkers will show hazards being flashed on all four exterior lights. In the cab when I blink the correct blinker is showing. However the hazards are blinking very dimly, also the tailights and the brake lights are very dim.
For future reference, just tie a piece of wire (bailing wire, or fishing line) to the connector before pulling it out of the column. When you remove the electrical wire the fishing line will follow.

Take the fishing line off the old connector and tie it to the new one. Pull it down into position when going back together and it will route itself into place just as before.

K


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Old 05-20-2017, 12:31 AM   #12
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That's exactly what I did actually which helped.
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Old 05-20-2017, 12:45 AM   #13
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Default Making progress :)
So today I replaced the front flashers which didn't seem to fix it other than they are brighter now and my stereo started working 😅 Which is odd but I'm not complaining. I decided I should try to tackle the dim portion of the issue so I got some LED lights for the brake lights as LEDs don't need as much voltage. That worked really well actually! Now if my headlights are off then my blinkers and brake lights work perfectly! The side markers are still dim but everything else is great! Now the blinkers in the front work all the time like they should. No more "hazards" same with the brake lights (which blink as I'm sure you are aware) but when the lights are on at all the rear flashers do not come on no matter what. Also the running lights do not come on only brake lights. The front flashers work perfectly fine though. I posted a video on YouTube for you guys so you can more clearly see what I'm talking about. The video is from before when I replaced the LEDs. I'll add another one tomorrow to show you what it's doing now.

https://youtu.be/bVheq21aQBk
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Old 05-20-2017, 12:51 AM   #14
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Originally Posted by chengny View Post
As a test, you can just switch the hazard flasher with the T/S flasher. If it works buy a new T/S flasher.

But, I can almost 100% guarantee you - that won't solve your problem.

If I had to venture a WAG, I would say that you have a cross connection between the LH & RH directional lamp feeds. When either side is selected, power is then supplied to both sides of the circuit (L/R & front/rear). Since both the hazards and the blinkers use the same filaments in each lamp, all of them start blinking. This gives the appearance of the hazards being operated.

I would start at the light assemblies themselves. Be sure that each socket has the correct lamp installed (1157) and that it is properly fitted into the socket.
Thank you! That makes a lot of sense actually! Because if it was providing power to both sides at the same time then it could make it appear dim as well. I'll look into that. Do you have any other suggestions about where to look for a cross connection?

Last edited by GMC86; 05-20-2017 at 12:52 AM. Reason: Re-wording a question to make more sense
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Old 05-20-2017, 04:37 AM   #15
 
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I would start by inspecting the entire length of the rear lighting harness. You don't have to tear into the harness loom. Just do a good visual check of the outside (corrugated) sheathing. The four leads that comprise the rear lighting circuits (YEL = LH T/S & Brake, DK GRN = RH T/S & Brake, LT GRN = B/U, and BRN = Parking, Marker & Plate lighting) are encased in a length of very durable plastic tubing. In addition, that tubing (along with the PNK lead to the gas tank sender) is encased within corrugated loom - for about half of the total run. The outer (corrugated) sheathing terminates when it emerges from under the cab. At that point, the PNK lead is connected to the sender and the hard tubing - that contains the rear lighting harness- transitions from the outside of the frame rail to the inside.

While tracing the harness, look for indications of exposure to high temperatures (i.e. melted areas of the plastic sheathing) and verify that it is not being pinched/crushed between structural components.





The most likely spot for heat damage to occur is where the tubing transits close to the exhaust system - pay particular attention to the section that runs alongside the muffler (if you have a muffler on the LH side):



After passing the muffler, the harness is fairly safe:



To do a shotgun test of the branch leads and associated sockets, locate the Weathertite style connector on the after side of the rear crossmember and disconnect the plug/socket. Try the directionals, brake lights, hazards, etc - whatever you are having trouble with (sorry, I didn't view the video yet). Of course none of the rear lamps will be working with the harness unplugged, but observe the front lighting group. If everything up front functions normally, you can concentrate on the rear lighting Christmas tree.

I would do this check first - it may save you a lot of time searching for a problem that doesn't exist.



The rear lighting Xmas tree layed out:



I have one strong suggestion - until you have found and rectified the cause of these issues, lose the LED's and return to incandescents.

You are going to confuse the issue by introducing an unstable variable during the diagnostic phase. Installing those LED's did not solve the underlying problem, it only altered the way in which in manifests itself. Get everything back to normal and then make the switch to LED's if you still want to. Just my thoughts.


As far as this:

So today I replaced the front flashers which didn't seem to fix it other than they are brighter now and my stereo started working

What do you mean by "replaced the front flashers"? Do you mean the 1157 lamps in the parking/direction assemblies?

Last edited by chengny; 05-20-2017 at 05:41 AM.
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