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Old 06-02-2015, 12:58 PM
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tapping onto brake switch wiring

I'm in the final phase of rigging my new Cherokee Latitude w/Active II for towing behind my motorhome. I did not order the Tow Package, as I wanted the 2.4 L engine rather than the 3.2L.

I've installed the tow plates (Blue Ox), and I've set up the Roadmaster 9160 Air Brake system with Breakaway. When the air brake is activated, the jeep brake lights also are activated.

As part of the braking system, I'm supposed to run a signal wire from the "cold side" of the jeep's brake pedal switch to an LED indicator in the motorhome. The dealer's Parts guy told me that a 4-wire connector attaches to the pedal switch, but he didn't know which wire I should tap. From the diagram, it looks to be either a Dark Green/Light Green brake signal wire (goes to "circuit B135") or a Dark Green/Yellow brake signal wire (goes to "circuit B134"). I haven't located either wire yet.

Can someone tell me which wire I need and where to find it?

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Old 06-02-2015, 11:32 PM
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Re: tapping onto brake switch wiring

Quote:
Originally Posted by MrK454 View Post
....

As part of the braking system, I'm supposed to run a signal wire from the "cold side" of the jeep's brake pedal switch to an LED indicator in the motorhome. The dealer's Parts guy told me that a 4-wire connector attaches to the pedal switch, but he didn't know which wire I should tap. From the diagram, it looks to be either a Dark Green/Light Green brake signal wire (goes to "circuit B135") or a Dark Green/Yellow brake signal wire (goes to "circuit B134"). I haven't located either wire yet.

Can someone tell me which wire I need and where to find it?
This isn't your Father's Oldsmobile.

In the old fashion brake switch a 12V positive wire went to the switch and a second wire (cold side) went from the switch to the brake lamps, or a relay that drove the brake lamps. The other side of the brake lamps were connected to chassis ground to complete the circuit when the brake switch was closed. You'd find the wire with 12V positive on the brake switch and know the other wire was the cold side.

Both of the wires you mentioned go to a circuit board in the Body Control Module. Are you sure either of these provide the 12V signal the air brake system needs? I realize that's a loaded question, but it is the question that would concern me. Also, owners are warned to not tap into the Cherokee's electrical system.

Maybe someone else has done this. Sorry I could not be of more help.
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Old 06-03-2015, 12:49 AM
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Re: tapping onto brake switch wiring

Go to the stop light. Definitely.

Cheers,
Steve
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Old 06-03-2015, 10:52 AM
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Re: tapping onto brake switch wiring

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Originally Posted by Barboots View Post
Go to the stop light. Definitely.

Cheers,
Steve
When you say "stop light", are you referring to the third stop light, the one at the center of the top of the rear hatch? I never thought of that, but since that light comes on only when the brake pedal is pushed, that's the sort of circuit I need.

Would you know where I might find (and identify) the 'hot' wire to the third stop light somewhere near the driver's area of the vehicle?

Steve, I see that you're Down-Under, and you have a Grand Cherokee. Might you know whether the GC and the 2015 Cherokee Latitude are similar with respect to wiring?

And THANKS for your suggestion. I hope you, or someone, can answer my follow-up question.

I'm going to start another thread, asking what types of braking systems folks have for their Toads, and how they've wired them.
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Old 06-03-2015, 11:34 AM
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Re: tapping onto brake switch wiring

MrK I was just passing by

Using a stop light circuit is just a change in approach which is required on pretty much any car these days. The brake pedal switch is often not 0V/12V now, they are often CANBus. Even if not, using it would not accomodate any advanced technology your car might be equipped with such as ESC (electronic stability control), TSC (trailer sway control), ACC (adaptive cruise control), FCW (forward collision warning), etc. As any of these systems must legally operate the brake lights, they will also operate your trailer brakes if connected to the lighting circuit. This is not possible via the pedal switch.

As far as which stop light... I don't know. On the GC the centre light is CANBus, so not appropriate. The outer lights are 0V/12V so work correctly. Use a multimeter to test prior to making any decisions. Down here we're all running a wire back to the left lamp... you've got to run a trailer brake wire anyway.

You can test the brake pedal switch if you think this all sounds like a crock, but also consider any tech you might have on board.

Cheers,
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Old 06-08-2015, 08:47 PM
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Re: tapping onto brake switch wiring

UPDATE: Technical Services from Roadmaster Inc. advises me to "locate the wire colors of Dark Green with a Light Green tracer and that should be the cold side of the brake switch."

I've finally located the connector at the top of the brake pedal, but I haven't yet tried to disconnect it. The wires are extremely small, and I don't want to take a chance on cutting or breaking any of them.

I will heed the advice I've been given regarding pulling the fuses to the braking system before I tinker with the wiring. Can anyone tell me what fuse numbers to pull?

I'm trusting Roadmaster to know what it's talking about, and I'll keep you informed as I gently work my way through this connection.
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Old 07-03-2015, 06:38 PM
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Re: tapping onto brake switch wiring

Any updates? Im at the same point. I need to find a location for a cold wire to hook up my brake controller.
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Old 07-03-2015, 11:41 PM
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Re: tapping onto brake switch wiring

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Originally Posted by sminker View Post
Any updates? Im at the same point. I need to find a location for a cold wire to hook up my brake controller.
My apologies for not following up. Here's where I'm at:
I decided to follow Roadmaster's recommendations. I pulled out the brake switch in order to disconnect the wiring plug. The dark green wire with light green tracer is indeed the wire I was looking for. I stripped a short section of that wire and wrapped my wire to the motorhome's LED around it. I tried to solder the wire, but apparently I'm not dexterous enough to stand on my head and hold a soldering gun and get the solder to hold the wires together. After reinstalling the plug onto the switch and reinstalling the switch, I confirmed that it was putting out 12 volts when the brake pedal is depressed, but my connection came loose. I haven't yet gotten back under the dash to finish the project.
A WORD OF CAUTION: The brake switch is self-calibrating, and you must NOT depress the brake pedal when re-installing it, otherwise it will not come 'on' unless the pedal is fully depressed.
Sorry about the lengthy explanation. The short answer is that the green on green wire is the wire you are looking for.
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Old 07-07-2015, 10:58 PM
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Re: tapping onto brake switch wiring

This is enough headache to cause someone to consider another auxiliary braking method for the Cherokee or any new toad that includes complex electronics. The other thing that would bother me about tapping into that wiring (besides the manufacturer's specific warning about tapping into the electrical system) is it goes to the Body Control Module where who knows what's going on in there since it includes non-serviceable circuit boards.

If it turns out playing havoc with the electronics, another method would be to tap off the top center brake light using a diode and a relay (for isolation and minimal current draw on the brake light circuit) to send the 12V current needed from the 12V outlet wiring in the trunk of the Jeep.
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Old 07-08-2015, 08:45 AM
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Re: tapping onto brake switch wiring

Quote:
Originally Posted by Array View Post
This is enough headache to cause someone to consider another auxiliary braking method for the Cherokee or any new toad that includes complex electronics. The other thing that would bother me about tapping into that wiring (besides the manufacturer's specific warning about tapping into the electrical system) is it goes to the Body Control Module where who knows what's going on in there since it includes non-serviceable circuit boards.

If it turns out playing havoc with the electronics, another method would be to tap off the top center brake light using a diode and a relay (for isolation and minimal current draw on the brake light circuit) to send the 12V current needed from the 12V outlet wiring in the trunk of the Jeep.
The real headache comes from my own lack of dexterity to make a clean, solid connection. And had I bought the trailer towing package on my Cherokee, I could have easily tapped into the wiring harness for the trailer brake. 20/20 hindsight.

Please keep in mind that this auxillary braking system works WITHOUT tapping into the brake wiring. The sole purpose of this connection is to light a single LED light on the dash of the motorhome to let me know when the brake is applied, and equally as important, that the brake is released when I let off the brake pedal of the motorhome. I wouldn't want to drag the toad vehicle with its brakes stuck in the applied position.

As I understand it, the line (green on green wire) feeds three circuit boards. Tapping into the wire before the circuit boards would equally affect them, while tapping into a wire downstream from one of them might create an imbalance that could throw a trouble code. I believe Roadmaster has researched the electrical issues and if there is a problem, I would look to them to resolve it.

The addition of a relay and diodes has proven successful when adding an aftermarket system for trailer hitch wiring, but I doubt that a single LED will draw any more current than the relay. I'll find out how Roadmaster's recommended wiring works, and will report back here--after I re-attach my wire. (I'll bet that the professionals use those clips that cut into the wire for their connections. I considered that, but not knowing how large the green/green wire is, I was afraid I'd cut it in two, hence my ill-fated attempt to solder the wires.)
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Old 07-13-2015, 06:15 PM
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Re: tapping onto brake switch wiring

The aux brake system I am using communicates 2-way via RF with a remote device in the motorhome. It communicates brake events and brakeaway events without need for wiring. I can appreciate the value of a wired system, but you are not the first person having difficulty tapping into the brake switch on the Cherokee.

As far as the draw on a circuit, I agree that a single LED will probably not be an issue, however the resistance drop over the wire might be, especially if the wire stretches the length of the car and the motorhome with a connector in between.
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Old 08-10-2015, 09:53 AM
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Re: tapping onto brake switch wiring

I hope this will be will wrap up this thread. I FINALLY got back under the dash to re-attach my sensor wire to the green-on-green "cold" brake system wire. This time, I made the connection with a blue-colored clamp-on connector (for 16-18 gauge wire), and taped it up so it shouldn't come apart. I tested the circuit with the multimeter and found the desired 12-volt output when applying the brakes.
Since I was also concerned that applying a load to the circuit might either create some sort of imbalance or possibly blow a fuse, I wired a lightbulb into the circuit. This bulb draws 0.94 amps, considerably more current than I imagine the LED in my motorhome will draw. The bulb glowed brightly when the brakes were applied. I then started the jeep, and was relieved that no trouble codes were present.
I want to thank everyone for their advice and counsel as I muddled my way through this project. As was said, the technology that is involved is new, and it doesn't provide any comfort when Jeep advises against making any modifications to the electronics. Thanks again to all of you.
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