M818 brake light switch

[benders]

I am new to this forum and new to military trucks. I am working on a 1970 Am General M818 6x6. The brake lights are stuck on, i tested the brake light switch and it was closed all the time allowing voltage through it. I installed a new one and the lights are still stuck on. I tested the new switch and it works properly. The brake light switch is tees into what I believe is a double check valve, the double check valve has a fee from the air/hyd assist cylinder and a feed line from another double check valve. Below is a link to a pic of the "double check valve". Its teed into where line#2 connects. There is air psi present at line#4 all the time which is why I believe the stop lights are on all the time. My best guess is the check valve is faulty but im not 100% sure of its function. The second lik is to a pic of where I think the stop light switch is suppose to be mounted. Any help would be greatly appreciated, I am a journeymen hd mechanic but very new to military trucks. Thanks

DOUBLECHECK VALVE REPLACEMENT cont'd

STOPLIGHT PRESSURE SWITCH REPLACEMENT (Contd]

 

[Hammer]

No offense meant by the simple suggestion, but is the trolly brake off? The lever on the right side behind the steering wheel should be in the 'up' position, which is pointing to about 1 o'clock.

 

[benders]

Im not sure but dam good point. No offence taken. Sometimes we over look the obvious. I gonna head to the shop to check that out because its gonna bug my ass all day. Thanks

 

[Hammer]

Hope it is that simple.
And that is one of the few things that will hold air pressure there, keep the brake lights on, and not engage the truck's service brakes.
Also note, if it IS on, when you push the lever up, you should HEAR the air releasing. If not, there might be other problems there as well.

 

[Ferroequinologist]

Are they on all the time? or only when the truck has air pumped up? I had a stuck upper cylinder in my air pack (hydraulic one that opens the air valve) and it was causing my lights to say on and drag my brakes.

 

[benders]

Big thanks to Hammer, I went to the shop and the trailer hand valve was half applied. I turn it off and the lights are now functioning as they should. Thanks very much for the help.

 

[Hammer]

Great news! I always like it when it is something simple (and cheap!)