Brake Lights Suddenly Not Working

[Vamoose]

I thought I posted this last night, but this morning I can't find it... sorry if this is a duplicate.

I've read many posts about brake lights not working, but none of them seem to hold the solution to my issue. Thanks for taking the time to read this. I'm pretty handy, but electrical problems are not my forte', to put is mildly.

I have a 43' HR Navigator and tow a 2010 Honda CRV. A couple of trips ago, I was towing when I noticed the brake lights not working. Later on the same trip, the running lights stopped working. I suspected the lighting cable to the toad and took apart the 4-pin connector. Sure enough, a couple of wires were loose. I tossed it out and bought a new one. I replaced the burnt fuses in the coach, which were located in the front fuse bay under the driver's seat.

With all the lights working fine, I figured that problem was behind me. I was wrong...

Last weekend we were in Tucson, a 3 hour drive away. Before coming home, I hooked up the toad and did my usual checks - all lights working correctly. At home, I disconnected everything and parked.

But now, as I prep for another trip, I discovered that the brake lights do not work again. The running lights and turn signals (separate yellow lights) work fine.

I checked the fuse and it is good (I found only one "Brake Lights" fuse which is located, as I said before, in the electrical bay under the driver's seat). In the rear passenger side fuse bay, I found a relay labeled "Brake Lights". I temporarily replaced it with an identical relay from another position - still no lights.

I pulled out the generator and found what I think are two pressure switches that I believe are activated when pushing the brake pedal. Please see the photo - are these indeed the pressure switches? Can anyone explain, in simple terms, how the brake light system works? From what I gather, pressing the brake pedal increases the air pressure, which activates the pressure switch (two of them?), one of which activates a relay, which energizes the brake lights... is this about right?

In reading a different thread, someone mentioned that if you blow a brake light fuse, you might also damage something called a "coverter". I have no idea what this is, how it works, where it is located, or how to check it. Thoughts?

I suppose my next step is to test the pressure switch, which I believe is a simple process. Any other suggestions????

Thanks in advance for your time and help.

Judd

[HarryStone]

Unless I'm wrong, your air brakes activate by the releasing of air pressure, not an increase in pressure, hence, your rig won't move if the air pressure hasn't built up. Regardless, the switch is a simple one, off, it doesn't pass power, on, it does. Get a meter and check for 12 VDC on one side of the switch (either side), then activate the brake pedal, and check that the switch passes power to the other side of the switch. One switch is likely for the park brake, and the other one for the coach brake lights.(Only guessing here)

[Skip426]

Originally Posted by HarryStone

Unless I'm wrong, your air brakes activate by the releasing of air pressure, not an increase in pressure, hence, your rig won't move if the air pressure hasn't built up. Regardless, the switch is a simple one, off, it doesn't pass power, on, it does. Get a meter and check for 12 VDC on one side of the switch (either side), then activate the brake pedal, and check that the switch passes power to the other side of the switch. One switch is likely for the park brake, and the other one for the coach brake lights.(Only guessing here)

Harry , the park brake is spring activated and air released .So no air pressure the coach won't move .
Service brakes are air pressure activated and spring returned .

[wolfe10]

Originally Posted by HarryStone

Unless I'm wrong, your air brakes activate by the releasing of air pressure, not an increase in pressure,

Yes, you are WRONG.


Service air brakes are applied by air pressure.


The parking/emergency brake is spring applied, air released.

[Rob_M]

Originally Posted by wolfe10

Yes, you are WRONG.


Service air brakes are applied by air pressure.

Adding to this…. And the parking brake is applied by the release of air pressure.

[Skip426]

Judd; two brake light pressure switches is a redundant feature , to make sure the brake lights come on in the event of one pressure switch failure .
The pressure switches , also provide a signal to the engine ECM to shut off cruise control , so important that they are working to prevent the engine trying to maintain speed while your on the brakes .

In your picture your have pressure switches ( wires connected on studs ) and pressure sensors ( wires with spade connectors) with both attached to the same supply , the sensors would only provide a gauge reading when the service brakes are applied .
I don't understand this set up because , unless your coach has separate gauges for brake applied pressure and actual tank air pressure , you wouldn't get a tank pressure reading unless the brakes are applied.

My chassis the two brake light pressure switches are attached directly to the foot valve under the floor from the brake pedal.
The tank pressure sensors are in a separate location.

[Vamoose]

Okay, based on your ideas I checked some more items and took a better photo of the pressure switch and how the two switches connect to separate sources. (see attached pic)

I checked the voltage across the two posts of each pressure switch. In both cases, there was 12V to one post when the brakes were NOT depressed. Then I applied the brakes and checked again - both posts of each switch now had 12V. This leads me to think that they are both working correctly. True???

Next - I looked back by the trailer hitch and found what I believe is the "converter". I think the purpose of this device is to change the tow vehicle's electrics (brake, turn signals, running lights) into currents that the toad can use given that the lighting setup is different. If that is the case, and if I DID burn it out when the lighting cable shorted out a month ago, two questions:
A) would a bad converter also cause the coach brake lights to go out, or just the toad?
B) isn't it strange that the brake lights continued to work for awhile, but then stopped? Why would it take time for the converter to fail? Seems to me it might happen immediately.

Lastly, I went to the fuse marked "Brake Lights" and decided to check for 12V (electrical bay under driver's seat). I couldn't get a reading. Does this fuse only have current running through it when the brake lights are activated?

So, to summarize:

A) Brake lights fuse good
B) Brake lights relay appears to be good
C) Pressure switches working correctly (I think)

Any other thoughts???

[Skip426]

Thanks for the better picture ; I'm still confused about the sensor location ( that's OK I'm old and easily confused ).

You are correct the converter ( combiner ) at the rear of the coach takes , turn signal power and brake light power and puts them on a single wire for trailer /toad use ; where signal and brake are the same bulb.
So only the trailer/toad lights should be effected .

Do you have brake light power to the converter ?

Newer Freightliner and Spartan chassis have rear fuse and relay power distribution centers , it's possible your chassis wiring uses a similar set up and you haven't found all the fuses/relays involved in brake light operation , yet.

[153stars]

Play with the spades at the brake light relay again especially if single wires with female spades . I've had few issues with brake/em/L or R turn relay connections although mine are wire spades relays on front engine fire wall, not exactly clean area. Replaced one dead relay. Have a helper press brake aired up you should be able to hear feel it click , check one that works to compare. You should also be able to test across the coil connectors with meter ,to see if feed from brake is there. As well as supply 12v off the fuse on contacts side.
I don't think convertor should prevent main chassis brakes from operating besides shorting and taking out the brake fuse. Can you unplug it. Are the rest of the toad bright filaments lighting up. L-R and EM

[HarryStone]

Originally Posted by Skip426

Harry , the park brake is spring activated and air released .So no air pressure the coach won't move .
Service brakes are air pressure activated and spring returned .

Thanks for kindly setting me straight.

[vito.a]

I replaced the 2 to 3 wire trailer tail light converter on our coach a couple of years ago.
Our motor homes have separate brake lights and turn signals and trailers use the same light for a brake light or turn signal.
I used this one:
https://www.amazon.com/CURT-56196-2-...%2C184&sr=8-10

[Vamoose]

Thanks for the input Skip and co.

Some more info:

I tested the Brake Lights fuse (in the front elect box under drivers seat). It has 12V.

I tested the relay first by listening when the brake pedal was depressed. I did not hear a click. Next, I removed the relay and tested for power at any post with and without the brake pedal pressed - there was no voltage there under any circumstance.

Do you have any idea what feeds the relay? It seems like I need to work backwards from there to the fuse.

I've attached a pic of the powerless relay in the rear box. See the adjacent label that says "Brake Light Signal". Any idea what that is referring to???

Please let me know if you have any new thoughts on the above or beyond.

Thanks again,

Judd

[Vamoose]

I found this info, along with the attached schematic. Very detailed explanation of things, with an owner-made diagram. This guy does good work, even though I can't say I understand all of it. Please take a look.

Rick, I am at a loss as to what the ticking box might be, other than perhaps a sending unit associated with towed vehicle braking. It is possible that it looks at coach braking system pressure to detect actual application of the service brakes and the brake light signal from the hazard/brake light circuit to enable the braking signal to the towed vehicle brake system. That would be my guess. That could be how they keep the towed brakes from coming on when just the Jake or the exhaust brake is applied thus illuminating the brake lights, but not the service brakes.

The notation I used was FRP for Front Run Panel, which is the box on the outside of the coach under the driver's side window. Roof exit means the black and white wire exits that front run panel thru the roof of the panel, in that huge bundle, and up into the enclosure to the left of the drivers left knee. From there, I haven't researched its path.

In the drawing, the "Z" symbol is the operating coil of a relay. The horizontal parallel bars are the switching contacts of a relay. The dashed lines show where the contacts are in the circuit for the relay coils that operate them, and vice versa. So you can see that, coming down from the top, the 12 volt source on Board #6 in the front run panel comes thru the BRK LTS fuse #6 on board #6, then out from that board to plug J1, pin #12, to the brake pedal switches where you say you are seeing the +12 volts. Plug J1 is one of the large, round plugs on the forward wall of the FRP. (That terminal on board #6 also goes to the brake lights relay and thence on to the brake lights and the cruise control cancel function) The signal from the brake pedal switches then comes back into the FRP thru the same plug J1, on pin #17, and goes to the brake lights relay. It also exits thru the roof of the FRP to begin its journey to the tow brake plug.

On my drawing, you can see where a wire comes to the top of the brake light relay from the turn signal switch. That is where the hazard light input comes into the brake light circuitry. The hazard lamps are the same as the brake lamps on our coach.

I don't recall what those other two pressure switches are for, other than perhaps low pressure alarms. It may be that one set of pressure switches is for the brake lights control and the other for the cruise control cancel function. If it is the latter, then that would be the answer to the uncertainty shown on my drawing to the right of the "Brake Light" relay where it says, "Cruise Control Cancel?". My memory fails me on that one. Dang!

Each time I've made a drawing for our coach and its systems, it has been due to a problem that has come up. Unfortunately, once a drawing is started, it is sometimes hard to define where it stops, and when I was researching a problem with my brake lights several years ago, I did not need to research the cruise cancel function, so I did not confirm those circuits. So it could be from either where I've shown it with the question mark, or it could be from that second set of pressure switches you are seeing. We have those on our coach, too.
__________________
Jim & Angie, Boise, ID
2021 Entegra Esteem 27U
2017 GMC Acadia Denali

[Vamoose]

My problem has been solved, and so, to make this thread more useful to someone in the future, I'm going to spell out what was discovered...

The only thing I had NOT been able to check was the trailer wiring converter (aka combiner), located back near the hitch. Because I need to leave in 2 days for a trip, I decided to seek out a pro. I called B&M Bumper here in Phoenix to see if they could look at my wiring and brake lights. They had a light day and said bring it on down. So far so good.

The mechanic, a terrific gentleman named Luis, looked at it right away. He immediately discovered a 2nd fuse that, for some reason, I had never seen. It was sitting right next to the Brake Light relay in the rear elect box. This means there are two Brake Lights fuses, one in the front box and one in the rear. Although the front box fuse was fine, this one was burnt out. Yay! An easy fix so far.

Once replaced, the brake lights worked fine on the coach, but they were only working on one side of the toad. This seemed to Luis to mean that the converter had been damaged, collateral damage when the lighting cable (from coach to toad) had shorted a month ago. This is a very common problem.

He checked the converter and it was bad. Luckily, they had one in stock and within half an hour it was installed. Everything was back to working correctly.

The lesson here is that a short in the lighting harness can cause not only fuses to burn, but also may damage the converter. Another lesson is that just because you found a fuse marked Brake Light doesn't mean there isn't another one in a different place, so keep looking.

Thanks to everyone here on the board for their thoughts. I learned a lot through this process, and gained a little more faith in my fellow RVers.

Safe travels everyone!

Judd