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    Guest Message by DevFuse
     

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    Brake Light Staying On



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    10 replies to this topic

    #1 OFFLINE   jeffl1107

    jeffl1107

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    • Model:RD688S
    • Year:1997

    Posted 23 June 2010 - 03:55 PM

    Hey guys,
    Another question for you. Got be picking my hair out. Anyway, my brake lights are constantly on. I traded out the stop light relay with 3 others and it is still staying on. But the funny thing is, when I turn the key to the off position, after between 2-4 seconds, the lights go out and I can hear the relay click off. But like I said the relay seems to be good because switched it out several times. Where else could I look to troubleshoot this. Thanks for the help.
    Jeff
    97 Mack RD688S

    #2 OFFLINE   QCDriver

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    Posted 23 June 2010 - 04:30 PM

    Just throwing this out. How about the switch to the trolly brake valve?

    #3 OFFLINE   rhasler

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    Posted 23 June 2010 - 06:03 PM

    Just throwing this out. How about the switch to the trolly brake valve?

    Also check for built up dirt under the pedal that is keeping it slightly depressed. There are two brake light switches. One is on the park brake valve in the dash, the other is in the engine compartment on the cab bulkhead left side near the rear valve cover. Either of these could be shorted or bad.
    "Mebbe I'm too ugly and stupid to give up!"

    #4 OFFLINE   jeffl1107

    jeffl1107

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    Posted 23 June 2010 - 08:01 PM

    No dirt built up under pedal. So I will check the two switches. Thanks

    #5 OFFLINE   jeffl1107

    jeffl1107

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    Posted 10 July 2010 - 08:44 AM

    Ok about at my wits end with this thing. The brake pedal does not seem to have dirt under it. Seems to be ok. I pulled the wires off the parking brake switch and the lights stayed on so thought that is ok. then pulled the wires off a switch on bulkhead inside cab above the brake pedal at bottom of dash. Lights went out. Put them back on and the brake lights went back on. So I replaced that switch and still, the lights stay on.

    #6 OFFLINE   rhasler

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    Posted 10 July 2010 - 12:10 PM

    Ok about at my wits end with this thing. The brake pedal does not seem to have dirt under it. Seems to be ok. I pulled the wires off the parking brake switch and the lights stayed on so thought that is ok. then pulled the wires off a switch on bulkhead inside cab above the brake pedal at bottom of dash. Lights went out. Put them back on and the brake lights went back on. So I replaced that switch and still, the lights stay on.

    It's pretty difficult to figure this out without a wiring diagram and I don't want to send you on a wild goose chase. I would check the turn signal switch. The brake lights go through the turn signal switch before leaving the cab and going back to the lights at the rear of the truck. If you already replaced the switch make sure it is the right type. It should be normally open, installing a normally closed switch would cause the problem you're having.
    "Mebbe I'm too ugly and stupid to give up!"

    #7 OFFLINE   David

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    Posted 10 July 2010 - 06:03 PM

    Is the pedal coming back up all the way by it self?

    #8 OFFLINE   jeffl1107

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    Posted 12 July 2010 - 12:02 PM

    Yes, the pedal comes all the way up. There was no flickering or anything when I pulled on it or shook it.
    So, hear is the latest with it. I fooled around with it for a while yesterday and this is the latest. I went over to the fuse panel behind the dash on passenger side. I started pulling out the relay and I saw the lights starting to flicker. I then put it back in and stayed on again. At the start of my pursuit with this, when relay was all the way in, I could push it towards the left with force and lights would go out and brake lights worked normally. But when I let my finger off it went back to staying on. Pulled it out and they went out again. Pushed on the brake pedal worked normally. Pulled trolly brake and worked normally. Works normally with blinkers on. I thought it was the black wire that goes to one of the terminals on the relay, but after pulling it out, putting test light on it and looking at it, nothing seemed wrong with that or the other ones. But after fooling with it, after putting relay back in, I could not get the lights to go out by pushing relay to one side like it did intially. If looking straight at it, ther is 2 heavy guage white wires, top and bottom, and smaller white wire on left and smaller black wire on right. Tested all and grounds seemed good and hots seemed ok.
    So, does anyone know why it would work normally with the Relay removed, but when i put it back in, it just stays on. I know it cant be good to run it any length of time with no relay in it. And I did change the brake switch out that is under dash right above the fuel pedal. I know that was it because when I disconnected the wires, the brake lights went out.

    #9 OFFLINE   dunny

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    Posted 12 July 2010 - 01:14 PM

    Yes, the pedal comes all the way up. There was no flickering or anything when I pulled on it or shook it.
    So, hear is the latest with it. I fooled around with it for a while yesterday and this is the latest. I went over to the fuse panel behind the dash on passenger side. I started pulling out the relay and I saw the lights starting to flicker. I then put it back in and stayed on again. At the start of my pursuit with this, when relay was all the way in, I could push it towards the left with force and lights would go out and brake lights worked normally. But when I let my finger off it went back to staying on. Pulled it out and they went out again. Pushed on the brake pedal worked normally. Pulled trolly brake and worked normally. Works normally with blinkers on. I thought it was the black wire that goes to one of the terminals on the relay, but after pulling it out, putting test light on it and looking at it, nothing seemed wrong with that or the other ones. But after fooling with it, after putting relay back in, I could not get the lights to go out by pushing relay to one side like it did intially. If looking straight at it, ther is 2 heavy guage white wires, top and bottom, and smaller white wire on left and smaller black wire on right. Tested all and grounds seemed good and hots seemed ok.
    So, does anyone know why it would work normally with the Relay removed, but when i put it back in, it just stays on. I know it cant be good to run it any length of time with no relay in it. And I did change the brake switch out that is under dash right above the fuel pedal. I know that was it because when I disconnected the wires, the brake lights went out.



    They say that the the only dumb question is the one that is not asked! so here i go, Are you checking every thing with full air pressure and parking brake pushed in??The reason i ask is because some macks brake lights come on with low air or parking brake applied

    #10 OFFLINE   jeffl1107

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    Posted 12 July 2010 - 10:19 PM

    Correct you are, but yes, full air pressure with parking brake in. Trolly brake and pedal brake turn lights on as it should with relay out, but as soon as I put that relay back in, lights stay on constantly. I am now, to use a big word beyond my capabilities, befuddled!

    #11 OFFLINE   Mike Sheldon

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    Posted 20 July 2010 - 11:08 PM

    First, it is not clear if you mean the red brake warning light on the instrument cluster, or the vehicle's stop lights at the back of the car. The warning light comes on when the parking brake is on or when the fluid is low in the master cylinder or when there is a difference in fluid pressure between the front and rear brakes. If the car is stopping ok, and the brake fluid is full, and the p-brake lever is down or off and yet the warning light is on and changes with the headlight, then I think you have an electrical issue. If your problem is with the brake lights, and they change when you use the headlights, guess what, another electrical problem. Your instinct to take it to a dealer is probably right. Please add some more information. good luck.




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