Brake lights stuck on…

[AaronHorrocks]

Brake lights stuck on…

The brake lights on my M52A2 are staying on constantly. They’ll only turn off when the dash switch is turned to off. I suspect that the brake light switch is kaput, and that I’ll need a new one. Any advice out there?

 

[Memphisdoug]

Check the switch

It should be a simple check to see if your switch is bad. Unplug the wires from it and then use a ohmmeter or test light to see if it is making a completed circuit all the time. If it is, there is your problem. If it isn't, you'll have to look elsewhere.

 

[Hammer]

Dumb question, I know, but does the M52 have a trolly brake, and is it engaged?

 

[AaronHorrocks]

A trailer air brake? Yes.

When it's on, it's shifted down and hits my knee. I think it's just an air valve, and doesn't affect the lights.

 

[Hammer]

On the 818, the trailer DOES turn the brake lights on.

Question, if there is ZERO air in the tanks, are the brake lights still on?

 

[AaronHorrocks]

While I haven't specifically noted if there was zero air in the tanks when I checked the lights (it's not something I've thought of yet to eliminate) I'm quite sure that's not related.

 

[M813A1]

Are your glad hands hook up to the storage glad hands ?? If so it will back pressure a bit and cause your brakes to drag and may cause the brake light to stay on the Storage glad hands should have vents in them so they do not cause back pressure !! check the other thread about vented glad hand brackets

 

[Wolf.Dose]

Summery of above:
The brake light shwich might be worn, so permanent stop light.
Remaining pressure in the system will mean the master valve has some problems. If the master valve works propperly, some relais valves might stuck (very uncommon failure).
If you find the brake lines after the master valve are pressuire free with released brake pedal, it is the switch. If some pressure remains in the system, chage the master valve.
So far the diagnoses from the other side of the river Atlantic.
Wolf

 

[AaronHorrocks]

Are your glad hands hook up to the storage glad hands ?? If so it will back pressure a bit and cause your brakes to drag and may cause the brake light to stay on the Storage glad hands should have vents in them so they do not cause back pressure !! check the other thread about vented glad hand brackets

Considering this problem is a new development, I doubt that's it.

Anyhow I ordered up the switch and some replacement front axle boots, so I'll be doing some work on my truck soon here...

 

[AaronHorrocks]

I was out with the truck again this Saturday, and I couldn't get the brake lights to stick on. It magically healed. I tried for about 15 minutes to reproduce the problem, and I just couldn't. I suspect the kiddies that like to play on and in my truck fiddled with something that I just happend to put back in place upon my last walkaround/inspection.