Brake lights won’t turn off

[Laura & Charles]

Brake lights on the coach won’t turn off. Brake pedal, parking brake, abd ignition switch positions make no difference. The only way I can turn them off is to disconnect the chassis batteries. (Of coarse, that makes driving impossible.)

This problem began the moment the previous issue’s symptom ceased. (It’s always something, isn’t it?). That problem was the engine wouldn’t shut off. I can’t see how the two can be related, but it seems unlikely that one problem started when another one ended is just coincidence.
See thread “Recurring ignition switch problem” for the full story. But bottom line: the problem resolved when the isolator relay between chassis and house batteries started isolating again. No real intervention, just flipped battery banks off and back on.

 

[HueyPilotVN]

Just a thought but I had a similar problem that was caused by backfeed from the connection to the Jeep that I was towing. I added a diode to the line for the towed vehicle and solved the problem.

The battery on the toad was powering the circuit in the DP.

 

[Laura & Charles]

Thanks Bill! But this problem is while not towing. Just for fun (i.e. no real expectation), I put the umbilical on between coach and toad and, as I figured, the toads brake lights were on, too.

 

[Krazeehorse33]

I'm guessing the brake light switch gave up the ghost but that's just a guess.

 

[OldWEB]

Brake light switch or there is a wiring harness connector in the Electrical Compartment, VCG - Brown with the brake sw. power that controls the brake light relay BR-R19. Maybe pulling the relay should extinguish the lights?

EDIT: Attached shows F28 is the brake sw fuse
#2 - there is also a brake status relay R25 which I think gets the power from the brake switch...

 

[darsben]

Probably easiest to disconnect the brake light switch and see if they go out then troubleshoot from there

 

[John From Detroit]

I'm guessing the brake light switch gave up the ghost but that's just a guess.

That was the case on my Rig.. Thankfully still during the warranty period.

 

[Kirk]

I can’t see how the two can be related, but it seems unlikely that one problem started when another one ended is just coincidence.

No real intervention, just flipped battery banks off and back on.

As a career electrical service technician, I am very skeptical what you did actually corrected the original problem. Without some kind of wiring problem, I don't understand how the coach battery could keep the engine running. I believe that you have a diesel and those do not need any electricity to run, other than the electric fuel pump. Most diesel engines I'm familiar with have a fuel shutoff that the ignition key triggers when turned to the off position.

I'm guessing the brake light switch gave up the ghost but that's just a guess.

I too would start with that possibility as it is so easy to check. If it is disconnected the brake lights should go out, if that is where power is coming from. I would use my voltmeter to trace the possible sources for power to the brake lights. There should be some connector plugs in the circuit that you could separate.

 

[TheBar]

Brake Lights Stuck On? 9 Reasons Why & How To Finally Fix Them

 

[Gary RV_Wizard]

In a DP coach the brake light switch is part of the brake treadle valve, the thingie that puts air pressure into the brake lines when you push the foot peddle. I suspect that either the switch in the treadle vale has failed closed, or there is a wiring short near there. The brake light power source is always hot, even with ignition off, so a short or a closed brake switch will still light up the lights.

 

[Laura & Charles]

Park break pressure switch is the problem. Elusive to find, but finally located one in CA. Overnighted here (to Valdosta, GA) for arrival and installation tomorrow. Apparently there’s two (low and high limit). Replacing both.

Shout out to Kenda Truck Center of GA for diagnosing the problem!

Hats off to all here for the help and info.

.

 

[darsben]

I was just about to say that !

 

[Laura & Charles]

I was just about to say that !

I’m sure…
When I first called Kenda and asked if they work on RVs, the service manager said, ‘for some things.. wadda ya got?’. When I told her, she said, ‘oh yeah… it’s probably your air brake pressure switch.. we see that all the time on trucks’. She said it with such confidence, I was immediately optimistic that she was right; and she was!

 

[OldWEB]

Well I am happy it was an 'easy' fix, just sad I got into trouble trying to help when you had no intention of fixing it yerself....

 

[Laura & Charles]

Well I am happy it was an 'easy' fix, just sad I got into trouble trying to help when you had no intention of fixing it yerself....

Not at all. I don’t understand why you feel you got into trouble. I found the fuses and relays you pointed out. I know my way around a toolbox… just too old and stoved up to get into position to work on most things anymore. But I still poke around as best I can and, every once in a while, I can actually fix something.