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  #1  
Old 11-17-2014, 10:22 PM
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Brake Lights Not Working

Followed the wife home tonight & noticed she had no brake lights (2000 grand chero laredo w/ 4.0L). Fuse 24 is good & the bulbs are good.

What to check next....the switch on the brake pedal? Is this a known failure mode for these vehicles? All the rest of the lights work ok.
thanks,
Mike Sal

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  #2  
Old 11-18-2014, 03:40 PM
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Re: Brake Lights Not Working

To start with, are you sure that she was using the brakes.
If none of the brake lights work and the fuse is ok, i would first check the brake switch. It is adjustable.
You can even remove the connector from the switch and put a jumper wire between the two pins, to check for a switch problem.
If this all ok, check for voltage at the light bulbs. The lower brake lights are known for their bad contact of the light socket tabs.
Just checked the wiring schematics, but the fuse for the brake lights is # 23 on the junction block, not # 24.
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Old 11-19-2014, 09:57 PM
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Re: Brake Lights Not Working

I'll try to check it out this weekend.....just got home from a business trip & have to go to the funeral home tomorrow night.....

I did stick my head under the dash to look at thw switch. It looks much different than the brake switches I'm used to. The plunger does move out when the pedal is pushed. I didn't know how often a jeep brake light failed in these vehicles.

Yes, I typed 24 when I meant 23 on the original post regarding the fuse.

Since all of the brake lights are not working, it's not likely to be bad contacts (and when I pulled the bulbs from one side, the contacts are very clean).
We'll see....
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Old 11-20-2014, 03:44 AM
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Re: Brake Lights Not Working

It can be that the switch plunjer is not moving out enough to activate the switch contact. I had this happening once after bleeding the brakes. Attached two pages with switch test info and adjustment info.
The problem with the light bulb sockets is not that they get dirty, but the small tabs just don´t make good contact with the board. Sometimes you will have a combination of a burnt lamp in one and bad contact in an other, so look at both. Regarding ground, the left and top brake light use one ground, while the right brake light uses a separate ground.
Be aware that if the brake switch is not adjusted well, that also the cruise control will not switch off when braking, so could give unpleasant surprises.
Attached Files
File Type: pdf Brake switch.pdf (140.0 KB, 9 views)
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Old 11-20-2014, 01:00 PM
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Re: Brake Lights Not Working

Thanks a lot for the diagram.....I was wondering how to remove the switch from the bracket. I went by the junkyard & bought another switch (3 dollars), but it was already disconnected from the bracket, so I couldn't see how to remove it.

I'll check both switches & see how they compare.
Mike S
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Old 11-20-2014, 03:42 PM
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Re: Brake Lights Not Working

Good news, the old switch was definitely bad & the salvage yard switch is still good. If I can attach the photo, you see the contact box I'm holding should have 3 metal tabs sticking up. The one that runs the brake light contacts stress cracked & fell off (it's the part laying down on the piece of paper.

I'm sure glad it was the switch, as I feared it would be a short somewhere that could be a pain to track down.
Mike S
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File Type: jpg 01 brake switch.jpg (52.0 KB, 7 views)
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Old 11-20-2014, 10:49 PM
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Re: Brake Lights Not Working

Arrrgghhhhh......I'm not done yet......

When I replaced the brake switch & stepped on the brake pedal, the brake lights all came on & I thought everything in the world was good again......

Tonight, following the wife home again, after dark with the lights on, I noticed that when she stepped on the brakes, only the 3rd light (at the top of the hatch) came on, and the tail lights went out. If the lights are turned off, the brake lights work ok.

I checked the bulbs again after we got home & they still check good. Where should I look now to figure out this puzzle???
Mike Sal
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Old 11-21-2014, 03:47 AM
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Re: Brake Lights Not Working

This really sounds as the famous socket tabs which don´t make good contact. First be sure that the light bulbs are ok. If they are, then bend the small copper coloured tabs a bit out and try again. I had it happening that i bend those tabs and the lights where working for a few days and then went out again. After a few times a just bend the other side of the light assy a bit out and then they never failed again.
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Old 11-22-2014, 11:03 AM
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Re: Brake Lights Not Working

Ok, Cleaned the contacts on the sockets (they were very clean to begin with) and even installed new bulbs (just because I already had them), but no change. If the headlights are turned on, stepping on the brake pedal will make the tail lights stop working and the brake lights stop working (with the exception of the "third" brake light on the hatch....it always works ok).

I probed the electrical connections & find that of the 5 pins, 4 of them show continuity to ground. The attached photo is the only terminal (on both sides of the car) that does not show continuity to ground.

I'll go back now to see which pins show any voltage when the pedal is pushed......
Mike S
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Old 11-22-2014, 11:19 AM
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Re: Brake Lights Not Working

Pin 6 is the voltage supply for the brake lights. Did you bend the small tabs from the light sockets out? It is normally not a problem of dirt or corrosion overthere, but the distance between the tabs and the circuit board.
Attached Files
File Type: pdf Left rear lamp assy.pdf (33.4 KB, 9 views)
File Type: pdf Right rear lamp assy.pdf (34.4 KB, 7 views)
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Old 11-22-2014, 11:34 AM
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Re: Brake Lights Not Working

Ok, with the lights on, I have 12v at upper right terminal. Stepping on the brake pedal (with lights on), I also have 12v at upper left terminal. But....if I plug the lamp assembly back into the connector (again, with both lights on and brake activated), I get no lights.

Which terminal is supposed to be the common ground? Why did I have continuity with these terminals (to ground) when the power was off?

Where is the harness grounded to the chassis? Do I have to start pulling the interior panels at the back to chase the wires?

I find it odd that this problem happened at the same time the brake light switch went bad, but I don't see how they would be connected.....any thoughts???
thanks,
Mike S
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Old 11-22-2014, 11:51 AM
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Re: Brake Lights Not Working

thanks for the diagrams. If the little tabs were not making connection, the lights wouldn't work at any time.....which mine do, as long as they are not used at the same time.....
Mike S
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