Brake lights won’t go off

[Matt0608]

Hello everyone,

I recently discovered that my brake lights come on when I turn on the chassis battery disconnect and stay on until the disconnect is turned off.

I also now have a coach which will not rev beyond 1,500rpm or travel faster than 9mph. After a bit of research, I believe my problem is the result of the King Cruise Control Module getting an invalid brake signal and going into “safe mode,” which doesn’t allow the module to pull the throttle cable very far. It pulls it just long enough to generate the 1,500rpm.

I found this really great web page explaining it all.

My next step was to search the schematic and locate the associated pressure switches.



The following switches are located in the forward bay under the driver’s seat.


This is my interpretation of the switches as compared to the schematic.


I clipped my test light to the chassis frame for ground and touched the nut which I labeled 12V DC in green. If I am understand things correctly, my test light should, and did, illuminate, regardless of brake pedal position as that is the source of power for the pressure switch in question.

I next touched my test light to the nut I circled in blue and found the light also turned on. Again, if I am understanding thing correctly, this should NOT happen without the brake pedal being pressed. I am calling this a failed pressure switch in need of replacement. Do y’all agree with this assessment?

My next question is if this pressure switch is in need of replacement, does anybody know what I should be replacing it with?

If not, I am going to pull the switch out and attempt to find the specs on the switch itself in hopes of finding a replacement. This leads me to my final question.

If I pull this switch out, will my brakes still work? I am hoping it will only effect the brake lights and not the brake actuation itself. My problem is that I have to pull my coach out of the storage unit in order to get into this bay. If my brakes won’t work, it will be stuck there in other peoples way until I can return with a replacement switch.

Thanks everyone. I look forward to hearing from y’all.

[twinboat]

Yes it seems at least one switch is stuck closed.

Isolate them, by removing the wires under the nut, to find the bad one.

If you remove a switch, you will have an air leak only when applying the brakes. It won't be bad enough if only jockeying the MH around the storage yard.

I'm pretty sure you could pick up a 1/4" MPT plug, to fill the hole, removing the switch will create. Then you would have no leak at all.

[Matt0608]

Thanks twinboat. The MPT plug idea is a good one so I will definitely give that a try.

Is this a fairly low pressure switch making standard teflon tape an acceptable choice?

Lastly, what is that black wire coming off the left pressure switch for? Something to do with that 5 watt resistor on the schematic maybe?

Thanks

[twinboat]

The new switch may come with thread sealer already on it otherwise Teflon tape is fine.

Can't help with the wiring.

[Skip426]

Two pressure switches ; is a feature to give you brake lights in case of a air line rupture in the front or rear air brake systems , that would mean no pressure on that 1/2 of the brake system and no brake lights to shut down the cruise control .

Nothing worse that being on cruise control and going for the brakes; and having the engine go WOT trying to maintain speed.

[TR4]

Originally Posted by Skip426

Two pressure switches ; is a feature to give you brake lights in case of a air line rupture in the front or rear air brake systems , that would mean no pressure on that 1/2 of the brake system and no brake lights to shut down the cruise control .

Nothing worse that being on cruise control and going for the brakes; and having the engine go WOT trying to maintain speed.

I learn something new every day, thanks for posting!

Bill

[stonegully]

I had a similar problem though mine did not effect speed.

It happened on our very first night on the way to Alaska, which was our first trip of more then 3 days. I called country coach and they gave me a part number. Sorry, I don't have it. I stopped by Freightliner and they had the part. Boy did I luck out as we did not pass many parts dealers for the next 10,000+ miles.

[stonegully]

Forgot to say, I had a 2000 Intrigue. My mechanic at home said I may get lucky by tapping the switch, it may fix the problem. It actually did for the moment till I hit the break again.

[Matt0608]

Originally Posted by stonegully

Forgot to say, I had a 2000 Intrigue. My mechanic at home said I may get lucky by tapping the switch, it may fix the problem. It actually did for the moment till I hit the break again.

I thought about giving it a whack.
Being so short on time to work on the coach, I ordered this switch without being able to get the other one off the coach to inspect. It was cheap enough to take the gamble. That switch won't come in until next week though.

I might try to get to the coach tonight to give it a good thump. I'd like to see if it fixes the switch enough to deactivate the brake lights. At least then I'd know if the low rpm problem will be resolved with a working switch.

[Matt0608]

I finally got a chance to come back out to the coach today to check on the pressure switch situation and found things aren’t going to be quite as easy as I had hoped.

It turns out, the reason I had the test light come on was because I am getting voltage from both the red and yellow pair of wires.

[IMG][/IMG]

The wires aren’t removed in this image, however, when I did take the yellow pair off of the switch, I still get 12VDC when touching them. If I am interpreting the schematic properly, these should be going to the brake lights and should have 0 Volts when not connected to anything. I’m thinking short to power which sounds terribly challenging to locate.

Any ideas?

[phays]

Are you saying that you removed the yellow wire(s) on the upper right of the right hand switch? The only way that wire would have 12 volts is if you are back feeding 12 volts from the brake light relay on the front run board. Since that wire goes to the relay coil and the other connection to the relay coil is to ground there is no 12 volt source for the yellow wires from the relay.

Could be the reason your bake lights are on all the time is the brake light relay on the front run board has fused contacts. Try removing the relay and see if the brake lights turn off. If so, with the relay removed, test the resistance with a VOM across terminals 30 and 87 on the relay. there should be infinite resistance since the contacts should not be connected together.

BTW, what year, model, and number for you coach? I don't think it really matters for your brake light circuits but some components may be in different locations.

[Matt0608]

Originally Posted by phays

Are you saying that you removed the yellow wire(s) on the upper right of the right hand switch? The only way that wire would have 12 volts is if you are back feeding 12 volts from the brake light relay on the front run board. Since that wire goes to the relay coil and the other connection to the relay coil is to ground there is no 12 volt source for the yellow wires from the relay.

Could be the reason your bake lights are on all the time is the brake light relay on the front run board has fused contacts. Try removing the relay and see if the brake lights turn off. If so, with the relay removed, test the resistance with a VOM across terminals 30 and 87 on the relay. there should be infinite resistance since the contacts should not be connected together.

BTW, what year, model, and number for you coach? I don't think it really matters for your brake light circuits but some components may be in different locations.

You are understanding the correct wires I am speaking of and that is exactly what I mean. I will have to do a little research to figure out what the front run board you mentioned is and where to find it.

Thanks! It would be great if simply replacing a relay fixes the problem as opposed to having to track down something tough like abraded wires.

[twinboat]

Could be the trailer plug shorting the charge line wire to the brake light wire or engine brake holding brake lights on.

[phays]

The front run board is in the bay under your driver's seat. There are 5 relays. Three above two. The brake light relay is the one on the right in the bottom row. At least that is the way it is in my coach.

Still don't know what coach you have.