E-brake light stays on

[JPMcCormick1]

I have a 2003 M1045A2 that has had the e-brake light on ever since I purchased it a year ago (the light on the dash). I am trying to figure out what the problem might be and have tried the following. I read in another forum to disconnect the cables on the switch connected to the e-brake handle and see if the light goes out and also disconnect the connector on the master cylinder. Neither action caused the light to go out. Does anyone know how these two switches are suppose to work. Are they suppose to create a continuous connection when working properly or open connection. I am thinking if it is a simple closed connection that if I connected the two wires would that create the same signal as a properly working switch or do I risk shorting something out.

I also want to order a replacement switch for the e-brake but have found 2 switches that look identical yet one is called the "Parking brake switch" part number R12356704 for $47 and the other is called the "neutral safety switch" for $5 part number 12338434. Are these interchangeable? They sure look exactly the same.

I also read https://www.logsa.army.mil/psmag/archives/PS2009/678/678-12.pdf which discusses bleeding the brake lines. Before doing that I was wondering is there was a way to fake the switch on the master cylinder to think it is working properly so I know for sure that might be the culprit before going through that.

Any other suggestions are welcomed.

 

[Wire Fox]

EDIT: I actually just realized that I had fundamentally misunderstood the positioning and trigger condition of the brake warning switch. I had assumed it was on the parking brake lever and only served as a simple cutout switch there. You can still try the test I listed below on the switch and you may find that the switch still works as I described (definitely, if it cycled between connected and not-connected when you change the parking brake lever positioning, it's working fine). I still think that you're probably looking at a case of a pinched ground wire, but it may actually be that your brake system is malfunctioning. I'd suggest reading the troubleshooting steps in TM 9-2320-387-24-1. It's a flowchart that gives you a series of steps to test if certain conditions are met. It will cover a lot more detail than what I can cover here.

Edit again: So I re-read the schematics and see...both the brake warning lamp switched (on the parking brake lever and on the master cylinder) are normally-open. Both of them serve the purpose of connecting the lamp to ground. Both should only do anything to the circuit if the master light switch is in a service position. If the light is still on while you have BOTH switches disconnected, you definitely have a wire pinched somewhere. If it's only one or the other, investigate those troubleshooting steps I've mentioned, or try to use some of what I wrote to help you understand the system. Please let us know what you find, as I'm very curious now!

I saw this yesterday, but was travelling and couldn't look at schematics...

Speaking purely on what I see written in the schematic (there's a very high-quality schematic in the back of TM 9-2320-387-24-2), the e-brake warning lamp should only be engaged if the following two conditions are met: the master light switch is set to one of the service lamp positions (non-blackout) AND the switch on the e-brake is pressed. The switch is normally-open and will close (connect) when the lever is UP for the brakes to be engaged. You're correct that disconnecting that switch should have made that light go out. You can test this switch with an ohmmeter. Disconnect both wires and connect each probe of the ohmmeter to each wire. While the parking brake is disengaged, the ohmmeter should show infinite resistance (no connection). While the parking brake is engage, the ohmmeter should show nearly 0 resistance (some meter will readout "SHORT"). If the switch operates this way, it's fully functional and not the problem!

As an additional note, the neutral safety switch is also a normally-open switch with a similar-sized load. I do not know if the switches have the same dimensions, but they do have the same electrical purpose. At a minimum, their part numbers will be different because the wire have the crimped-on metal labels that have the wire # engraved on them. If you don't mind these numbers being wrong, you may be able to substitute the switches. But at the same time...I don't think the switch is your problem.

Clarification question: Is the indicator light on ALL OF THE TIME, or is it only on when a certain combination of conditions are met? (Light switch on, engine running, etc...)

My guess as to what's wrong, if the lamp is only lit when the Master Light Switch is in one of the service drive positions: A wire is damaged, causing the indicator to be grounded to the body 100% of the time. The parking brake switch is switching the "ground side" of the circuit, meaning that a one of these wires being pinched or frayed and touching any metal would result in the circuit "thinking" that the switch is closed and the light should be on. One wire of the indicator will be fed from the master light switch. The other wire should be going under the vehicle to the parking brake assembly. Inspect the wire going under very closely at all points and look for bad connectors that may be contacting the body, a wire with a worn jacket, or especially a wire that has been pinched between some parts that were assembled.

 

[JPMcCormick1]

EDIT: I actually just realized that I had fundamentally misunderstood the positioning and trigger condition of the brake warning switch. I had assumed it was on the parking brake lever and only served as a simple cutout switch there. You can still try the test I listed below on the switch and you may find that the switch still works as I described (definitely, if it cycled between connected and not-connected when you change the parking brake lever positioning, it's working fine). I still think that you're probably looking at a case of a pinched ground wire, but it may actually be that your brake system is malfunctioning. I'd suggest reading the troubleshooting steps in TM 9-2320-387-24-1. It's a flowchart that gives you a series of steps to test if certain conditions are met. It will cover a lot more detail than what I can cover here.

Edit again: So I re-read the schematics and see...both the brake warning lamp switched (on the parking brake lever and on the master cylinder) are normally-open. Both of them serve the purpose of connecting the lamp to ground. Both should only do anything to the circuit if the master light switch is in a service position. If the light is still on while you have BOTH switches disconnected, you definitely have a wire pinched somewhere. If it's only one or the other, investigate those troubleshooting steps I've mentioned, or try to use some of what I wrote to help you understand the system. Please let us know what you find, as I'm very curious now!

I saw this yesterday, but was travelling and couldn't look at schematics...

Speaking purely on what I see written in the schematic (there's a very high-quality schematic in the back of TM 9-2320-387-24-2), the e-brake warning lamp should only be engaged if the following two conditions are met: the master light switch is set to one of the service lamp positions (non-blackout) AND the switch on the e-brake is pressed. The switch is normally-open and will close (connect) when the lever is UP for the brakes to be engaged. You're correct that disconnecting that switch should have made that light go out. You can test this switch with an ohmmeter. Disconnect both wires and connect each probe of the ohmmeter to each wire. While the parking brake is disengaged, the ohmmeter should show infinite resistance (no connection). While the parking brake is engage, the ohmmeter should show nearly 0 resistance (some meter will readout "SHORT"). If the switch operates this way, it's fully functional and not the problem!

As an additional note, the neutral safety switch is also a normally-open switch with a similar-sized load. I do not know if the switches have the same dimensions, but they do have the same electrical purpose. At a minimum, their part numbers will be different because the wire have the crimped-on metal labels that have the wire # engraved on them. If you don't mind these numbers being wrong, you may be able to substitute the switches. But at the same time...I don't think the switch is your problem.

Clarification question: Is the indicator light on ALL OF THE TIME, or is it only on when a certain combination of conditions are met? (Light switch on, engine running, etc...)

My guess as to what's wrong, if the lamp is only lit when the Master Light Switch is in one of the service drive positions: A wire is damaged, causing the indicator to be grounded to the body 100% of the time. The parking brake switch is switching the "ground side" of the circuit, meaning that a one of these wires being pinched or frayed and touching any metal would result in the circuit "thinking" that the switch is closed and the light should be on. One wire of the indicator will be fed from the master light switch. The other wire should be going under the vehicle to the parking brake assembly. Inspect the wire going under very closely at all points and look for bad connectors that may be contacting the body, a wire with a worn jacket, or especially a wire that has been pinched between some parts that were assembled.

Thank you Wire Fox. The e-brake light is on all the time once she in is run and irrespective of the service lights being on or off. The e-brake light is also on even when I disconnect the wires from the e-brake and from the master cylinder. Nothing I have disconnected so far as allowed the e-brake light to go off. I did test the switch with an ohmmeter and tried pushing the little ball inside and there was continuous connection either way so this leads me to believe the switch might have a problem however that does not explain why when the wires are totally disconnected from the e-brake switch the light still stays on unless there is a third parameter that would activate the e-brake light.

 

[Milcommoguy]

When I reversed engineered the PCB for my manual control box, there is a connection at " pin C" / body harness / PCB. This is for the "brake lamp test". It should be an "open" with a brief pulse going low (ground) to flash the brake lamp (led) when switched to RUN. This could be ?? your issue or has stated one of the "67 numbered" leads is pinched, frayed to a low (ground) keeping the lamp on.

Service Light Switch does not effect this circuit.

Overall a simple circuit to light the brake lamp... until one gets a fried PCB.

Drain the water out of PCB and see what happens, CAMO

 

[JPMcCormick1]

When I reversed engineered the PCB for my manual control box, there is a connection at " pin C" / body harness / PCB. This is for the "brake lamp test". It should be an "open" with a brief pulse going low (ground) to flash the brake lamp (led) when switched to RUN. This could be ?? your issue or has stated one of the "67 numbered" leads is pinched, frayed to a low (ground) keeping the lamp on.

Service Light Switch does not effect this circuit.

Overall a simple circuit to light the brake lamp... until one gets a fried PCB.

Drain the water out of PCB and see what happens, CAMO

Just to clarify this is not the rear brake lights that are lit it is the e-brake light on the dash board that is always lit.

 

[DREDnot]

Just to clarify this is not the rear brake lights that are lit it is the e-brake light on the dash board that is always lit.

I think what hes saying is regardless of the other two circuits(E-brake, and master cylinder) there is a Lamp test phase when you first turn the ignition switch to "ON" that powers that dash lamp to test it. Just like modern cars that light all the warning lamps and sweep the gauges at startup. If that circuit in the PCB has shorted out you could get the lighted lamp independently of the other two being unplugged

 

[papakb]

For some reason in the back of my mind I think the switch on the brake proportioning valve will also turn on the Brake warning light but I can't see it in the schematics. This is the little 2 pin connector on the top of the brake hydraulic splitter valve. I remember having it switch to one side when I had a bad brake line to the front brakes and it took me a while to find it. There's a little ball bearing just under the switch that moves forward or backward depending on where the hydraulic failure is that shorts that line to ground. Pull the connector off of it and see if the light goes out.

 

[Milcommoguy]

Nobody said anything about turn signals, brake lights, park lamps.

It's this one right??. >

As I stated... There is a circuit in the PCB that "winks" the warning dash mounted lamp to test it. It is just to the left of the steering wheel and shown above. Operator switches the ignition (but really not the ignition switch) from the STOP to the RUN position, one should get the "wink".

This will be the case with the proportioning valve or brake lever switches not closed (or hank-ied up). It maybe ?? the third circuit that is holding the lamp / led ON.

You stated you remove the two switch leads (proportioning valve and brake lever switches) Lamp should have gone dark.

Short of a SHORT circuit to ground in the number 67 wiring,.. IMO, your "wink" circuit is wack, CAMO

 

[JPMcCormick1]

I think what hes saying is regardless of the other two circuits(E-brake, and master cylinder) there is a Lamp test phase when you first turn the ignition switch to "ON" that powers that dash lamp to test it. Just like modern cars that light all the warning lamps and sweep the gauges at startup. If that circuit in the PCB has shorted out you could get the lighted lamp independently of the other two being unplugged

I do not think that would be the cause as I tried swapping out the PCB with another one and e-brake light is still on.

 

[JPMcCormick1]

Nobody said anything about turn signals, brake lights, park lamps.

It's this one right??. >

As I stated... There is a circuit in the PCB that "winks" the warning dash mounted lamp to test it. It is just to the left of the steering wheel and shown above. Operator switches the ignition (but really not the ignition switch) from the STOP to the RUN position, one should get the "wink".

This will be the case with the proportioning valve or brake lever switches not closed (or hank-ied up). It maybe ?? the third circuit that is holding the lamp / led ON.

You stated you remove the two switch leads (proportioning valve and brake lever switches) Lamp should have gone dark.

Short of a SHORT circuit to ground in the number 67 wiring,.. IMO, your "wink" circuit is wack, CAMO

I had a spare PCB on hand and did swap them out but still had the same problem. So I do not think it would be in the PCB itself.

 

[86humv]

Un-plug the plastic connector on your Prop. valve next to master cyl.

 

[JPMcCormick1]

Un-plug the plastic connector on your Prop. valve next to master cyl.

Are you referring to this one? If so I already tried that.

 

[86humv]

Probably EESS / PCB box

 

[JPMcCormick1]

Probably EESS / PCB box

But I already swapped for a new PCB box and same problem.

 

[86humv]

Un-plug switch at pedal.

 

[Milcommoguy]

Would be best to study up the TM 9-2320-280-20 wire drawing. Find the brake warning lamp assembly at the top and follow it thru. Wire #67 is the clue.

I give UP...poetry. Going to shovel snow in the desert.

CAMO

 

[JPMcCormick1]

Un-plug switch at pedal.

Interesting idea. I will try that tomorrow and post results.

 

[JPMcCormick1]

Would be best to study up the TM 9-2320-280-20 wire drawing. Find the brake warning lamp assembly at the top and follow it thru. Wire #67 is the clue.

I give UP...poetry. Going to shovel snow in the desert.

CAMO

There is no snow in desert, only sand that looks like snow

 

[Milcommoguy]

Thanksgiving morning. Tell me now... global warming. Snowed today too. CAMO

 

[JPMcCormick1]

Interesting idea. I will try that tomorrow and post results.

So finally got a chance to work on the e-brake light. Disconnected the brake switch at pedal and still light stayed on. Decided to disconnect the cable from the master brake cylinder and connect the connectors together to form a continuous connection and light went out. What is interesting is that now even when I no longer have the connectors together but have it disconnected from the master brake cylinder the light is still off. If I connect it back to the master brake cylinder light comes back on. When I originally unplugged it from master brake cylinder the light still stayed on. Not sure if connecting the terminals together reset something in the control box but now she seems to be displaying as should with e-brake light on when plugged in and off when unplugged. This obviously means there is an in-balance in the brake system that I will have to track down but at least I tracked down the cause of the e-brake light being on.