Pressure switches

Topic: Pressure switches (Read 1061 times) previous topic - next topic

Pressure switches

February 26, 2024, 09:16:06 pm

My cruise control will not disengage when you step on the brake pedal. There are 4 pressure sw's in the bay under the drivers seat. 2 are brake light switches, the othe 2 are marked NC 2 pole,. Does anyone have a clue what the sw are for and the part numbers for all 4 of them.

Re: Pressure switches

Reply #1 – February 26, 2024, 10:15:42 pm

I started looking for my invoice the first day I read this and I can't find it in my folder so I must have failed to file them. I had the no cruise disengage a couple years back and that was the culprit. I bought them at NAPA but I misplaced the invoice. Pretty common failure so surely everyone hasn't misplaced the invoice & part #.

Re: Pressure switches

Reply #2 – February 26, 2024, 10:24:14 pm

Mines 3 years older but the 2 for the brake lights are to the left of steering box left and facing me. The 2nd pair looking straight ahead in the bay and up higher I was told have to do with the retarder..... what I don't know but was told that.

Re: Pressure switches

Reply #3 – February 27, 2024, 09:56:03 am

Photos , the top 2 are the ones I'm trying to find out what they do.

Re: Pressure switches

Reply #4 – February 27, 2024, 11:19:44 am

Bruce
please keep us posted I've got a similar problem.

Thanks Tommy

Re: Pressure switches

Reply #5 – February 27, 2024, 03:01:36 pm

Ok so the bottom 2 round switches are the brake light switches. Going to replace them and see what happens. Those 2 switches apparently trigger several things, one is obviously the brakes lights, the outher is a relay to turn the brake lights on with the retarder, and im sure the cruise control shutoff. We'll see. Still hav no idea what the Hobbs switches feed, I'm assuming the retarder apply, as they are NC.

Re: Pressure switches

Reply #6 – February 27, 2024, 04:21:42 pm

Why not just test the air switches with a test light or a volt meter. One post on the switch should be hot
all the time and when you step on the brake the other post should be hot. These switches should come
on with very light pressure on the brake peddle. The cruise control shuts off when the brake lights come
on. One my coach the are three pressure switches that the contacts in the three switches come on at
different pressures so the retarder comes on stronger as more brake pressure is applied.

Re: Pressure switches

Reply #7 – February 27, 2024, 04:45:41 pm

Quote from: bbeane – February 27, 2024, 09:56:03 am

Photos , the top 2 are the ones I'm trying to find out what they do.

I the switches are hanging off of the brake treadle valve they are brake light switches ganged as a pair in parallel. A white wire labeled T3 feeds them.

Re: Pressure switches

Reply #8 – February 27, 2024, 05:00:25 pm

Peter, where are your 3 retarder switches located? My issue is intermittent and, affects the release of the cruse when the brake is applied. My retarder works as it should.

Re: Pressure switches

Reply #9 – February 27, 2024, 05:05:22 pm

Tim the switch's are located in the bay under the driver. They appear to be tied into the brake relay valves

Re: Pressure switches

Reply #10 – February 27, 2024, 06:22:20 pm

My retarder switches are on the left of the steering column. My brake light switches are under the
coach near the left front.

Re: Pressure switches

Reply #11 – February 27, 2024, 09:17:24 pm

Do brake lights turn on with brake pedal? Put a meter on pressure switches. Throwing parts on an undiagnosed problem is usually not a good idea.

Re: Pressure switches

Reply #12 – February 27, 2024, 09:39:03 pm

Barry, the problem is intermittent, when the problem happens a quick tap on the Brake switches and it works for a bit. Percussive diagnostics.

Re: Pressure switches

Reply #13 – February 27, 2024, 10:01:13 pm

Bruce there must be a relay to turn on the brake lights when using the retarder. I believe
mine is intermittent also but as I have a Jake brake I haven't bothered looking into it. I remember
a while back someone talking about not wanting the brake lights when using the retarder disconnecting that option.
So someone may know how to do it.

Re: Pressure switches

Reply #14 – February 27, 2024, 10:11:21 pm

Peter, there is a relay connected to the brake light sw(s) a friend that installed some of these at FT you just unplug the relay. The relay is a standard cube relay. Mine is located near the BL switches.

Re: Pressure switches

Reply #15 – February 27, 2024, 10:17:16 pm

Maybe that relay is flakily.

Re: Pressure switches

Reply #16 – February 27, 2024, 10:26:07 pm

Quote from: oldguy – February 27, 2024, 10:17:16 pm

Maybe that relay is flakily.

that could very well be, it too is getting replaced tomorrow.

Re: Pressure switches

Reply #17 – February 28, 2024, 11:25:14 am

One of the standard brake light configurations were two air pressure switches next to each other mounted on upper front metal wall in streetside forward compartment. Pressure switches were plumbed to front and rear air brake tanks (both tanks located above front axle). Wires would turn on rear brake lights when either pressure switch was closed. To turn on brake lights with just retarder activation, a standard Bosch cube relay was mounted next to pressure switches. When Allison retarder is activated, a retarder-relay mounted on the 12v panel in front of co-pilot seat closes. A wire from the retarder relay is run to the relay next to pressure switches. When this second retarder relay is closed it also turns on brake lights by being connected to the wires on the pressure switch.

Re: Pressure switches

Reply #18 – February 28, 2024, 12:27:53 pm

Do what are the 2 Hobbs NC switch's for? They are Teed into the same fitting as the BL SW(s)

Re: Pressure switches

Reply #19 – February 28, 2024, 05:32:33 pm

FYI, in some coaches under the dash behind the carpeted wall forward of brake pedal, are triple air pressure switches that each close at different psi ratings to activate different retarder levels as brake pedal is pressed. They do not turn on brake lights.

Re: Pressure switches

Reply #20 – February 28, 2024, 06:49:33 pm

I think the normally closed switches turn on the low air pressure light and buzzer.

Re: Pressure switches

Reply #21 – February 28, 2024, 11:44:09 pm

Quote from: bbeane – February 27, 2024, 05:05:22 pm

Tim the switch's are located in the bay under the driver. They appear to be tied into the brake relay valves

Ok..
This might help A-5412 and B-2193

For some unknown reason I cannot attach files....

Re: Pressure switches

Reply #22 – February 28, 2024, 11:45:59 pm

Quote from: bbeane – February 27, 2024, 05:05:22 pm

Tim the switch's are located in the bay under the driver. They appear to be tied into the brake relay valves

Ok..
This might help A-5412 and B-2193

For some unknown reason I cannot attach files....

Re: Pressure switches

Reply #23 – February 29, 2024, 01:19:45 pm

https://www.foreforums.com/index.php?media/item/ae-5412-2002-05-08-wtec-iii-interface.4578/

Re: Pressure switches

Reply #24 – March 08, 2024, 08:48:44 am

Quote from: bbeane – February 28, 2024, 12:27:53 pm

Do what are the 2 Hobbs NC switch's for? They are Teed into the same fitting as the BL SW(s)

Hey Billy, what was the final resolution to this issue?

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