Deuce Brake Light Operation Question

[mistaken1]

Way back when I checked my brake lights. Momentarily press the brake pedal and the lights light up. Good to go.

Last night I came home after dark. After passing through the gate I hit the gate opener button to close the gate and I pressed the brake pedal to use the brake lights to help me see in the dark to verify that the gate latched.

The brake lights came on but then a second later while still holding the pedal down they went off. I released the pedal and pressed it again and once again the brake lights came on and then again while still holding the pedal down they went off. I pressed harder on the pedal and they came on again but went off after a second.

So I got online here this morning and read many threads on brake lights and brake light switches. I have the air pressure switch and the place where the hydraulic switch would go is plugged (came that way from uncle sam).

One of the things I read on here (I apologize for not remembering who wrote it) said that the deuce brake lights only work when actually braking unlike a pedal switch that will activate the brake lights when the pedal is pushed irregardless of any actual braking action.

So my question is "When setting still is it normal for an air operated switch to actuate the brake lights and then go off after a second or so even while brake pedal is still depressed applying pressure to the wheels or do I have a bad pressure switch?"

Thanks in advance to taking time to read this and for sharing your knowledge.

 

[DieselBob]

Sounds like you might have a bad switch. The brake lights should remain on as long as you have pressure held on the brake pedal. I just changed to the air switch and as long as there is pressure on the brake pedal the brake lights are on steady. I take it that you are not having and low air pressure problems. With the air pressure up to 120PSI and the truck not running, if you hold pressure on the brake pedal do you hear any air leaks or does the air pressure start to drop ?

 

[mistaken1]

DieselBob, thank you.

The brakes seem to work fine. I do not notice pressure dropping when I apply the brakes nor hear any air leaking. When I release the brakes I hear air venting (I assumed something had to be done with the air pressure in the air pack when the pedal is released).

I will check it tomorrow with the engine off to listen for leaks.

When the brake light went off the pedal remained in the same place. I could push the pedal a little further because at the time I was stopped and I just pressed the brake pedal enough to see the brake lights come on.

 

[Tinwoodsman]

Look forward to hearing the results of this one. I am thinking about making the switch upgrade.

 

[DieselBob]

Look forward to hearing the results of this one. I am thinking about making the switch upgrade.

I purchased the upgrade kit from Erik's and it had everything needed. Was easy to do and one less thing in the brake hydraulic system to cause problems.

 

[mistaken1]

After parking the deuce I had soldier b press and hold the brake pedal. No leaking air under the truck. Maybe a little air leaking out the trailer service port. The brake lights came on and a a count of thousand one went off. Same deal as earlier.

I had read somewhere on here people who had NOS air pressure switches had to oil them to get them working again. I will try that next and if that fails then a new air pressure switch.

 

[rlwm211]

Check the gate valve on the service glad hand on the back. If it is open, and the glad hand gasket will leak some it can reduce the pressure enough to allow the switch to "drop out".

Worth a shot as the air operated switch is very reliable.

RL

 

[DieselBob]

The brake lights came on and a a count of thousand one went off. Same deal as earlier.

You said only one brake light went out, The other stayed on ? That would tend to indicate a problem with the wiring either ground or feed or even a corrosion problem with the lamp holder. If the switch at the airpack was causing the problem it would affect both brake lights equally. Maybe the turn signal unit is acting up. The turn signals and brake lights are controlled through that unit if I remember correctly. I would check and clean all the grounds first just to eliminate that as a cause.

 

[Jake0147]

The brake lights (in EITHER switch configuration) are activated by pressure in the braking circuit. With the original switch it is pressure in the hydraulic circuit. With the air update, it's pressure in the air assist circuit.

If your brakes are working, and the power assist is working, then there is pressure present. EVEN WITH A LEAK. If the supply (air supply from air system, fluid supply from the master cylinder) is great enough to maintain braking, then the pressure remains inside the tubing, and therefore acts against the pressure switch.

The remainder of the circuit is purely electrical, no electronics. Safe to say (but no guarantee of course) that the electrical system does not have a loose and jiggling connection that follows your actions this exactly for this long.

In terms of actuation, pretty sure you have what you need.
in terms of the circuits involved, pretty sure you have what you need.
Is Pretty sure close enough for you? Get a switch.
Wanna confirm it before you order out for stuff? Unplug the electrical connector from the brake light switch, rig up a jumper wire to connect the two wires directly to each other to duplicate a closed (turned on) brake light switch. Observe the lights. This will tell you instantly if the brake light switch is at fault. If so, get the switch. If not, then some assumptions will have to go away and it'll be back to systematic testing, volt meters, test lights, oscilloscopes, diagnostic engine analyzers, and X-ray scanning machines.

Well, maybe a test light. It's not a complicated circuit at all.

 

[mistaken1]

You said only one brake light went out, The other stayed on ? That would tend to indicate a problem with the wiring either ground or feed or even a corrosion problem with the lamp holder. If the switch at the airpack was causing the problem it would affect both brake lights equally. Maybe the turn signal unit is acting up. The turn signals and brake lights are controlled through that unit if I remember correctly. I would check and clean all the grounds first just to eliminate that as a cause.

Sorry that should have been "thousand-one" as in a count of one second when both lights go off.

The first thing I am going to do is pull the wires off the switch and jumper them to verify the electrical circuit is good. If it is (I suspect it will be) then I will remove the existing switch and try the air tool oil.

In the mean time I need to order an axle seal so I will order an air pressure brake light switch at the same time.

 

[DieselBob]

Have you had time to troubleshoot this any more. Just curious what was wrong.

 

[stumps]

Your air pressure powered brake switch has an air circuit sort of like this:

AIR------DIAPHRAGM----SPRING---SWITCH

On the SWITCH end, there is a cap that seals the SWITCH to the DIAPHRAGM, and keeps the elements out.

The DIAPHRAGM works with pressure differential. If the pressure on the AIR side is lower than the pressure exerted by the SPRING, the SWITCH is OFF. If the pressure on the AIR side is higher than the pressure exerted by the SPRING, the SWITCH is ON.

Imagine there is a hole it the DIAPHRAGM. Air can leak slowly through the DIAPHRAGM in either direction.

When you press on the pedal, the air pressure goes up on the AIR side, and DIAPHRAGM presses on the SPRING, and turns on the SWITCH.

...But...

You have a leak, which allows the air pressure on the AIR side of the DIAPHRAGM to slowly bleed into the SWITCH side, and pressurize the cap the covers the SWITCH and SPRING and keeps the elements out.

When the pressure difference between the AIR side and the SPRING side become small enough, the SWITCH will turn off.

When you take your foot off of the brake pedal, the AIR pressure goes away, and the air that leaked through the DIAPHRAGM leaks back into the AIR side, and everything is reset and ready for your next brake cycle.

In your case, the DIAPHRAGM leak takes about 1 second.

Get a new air pressure brake switch.

-Chuck

 

[mistaken1]

Have you had time to troubleshoot this any more. Just curious what was wrong.

Not yet. I will report what I find.

I did find that I have a Borg Warner S194 stop light switch which I bought way back when for the eventuality of my stop light switch failing but now realize is not what I need.

 

[mistaken1]

Stumps,

I am betting $5 that you are correct.

 

[Steaminjim]

My money is on Stumps! Best explanation I have read on an intermittent problem in a good long while. The jumper wire to eliminate any electrical problems or isolate the problem to the electrical side is also a great way of splitting the system in half to isolate the problem. Yea buy the switch.
Good luck