Can someone explain this wiring diagram to me please?

Captain Skip

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I'm setting up my JL to tow behind my motorhome. One thing I need to do is add a brake light disconnect system to the JL's brakes. It's a relay that goes inline on the wire on the brake pedal switch and prevents the JL's brakes from overriding the brake light signal from the motorhome. I need to cut the wire downstream of the switch that goes to the brake lights and install the relay in between the cut ends of that wire. Problem is if I read this diagram correctly it looks like there's 3 wires on the brake pedal switch. Obviously I don't want to cut the wrong one. Has anyone else added a brake light relay cutout on their JL for towing purposes and remember which wire you used? Or, can someone interpret this diagram for me? I'm not sure what I'm looking at here....maybe I'm looking at the wrong diagram?
Screen Shot 2020-10-21 at 5.10.54 PM.png

 

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Sensor Feed = Power
Sensor Return = Ground/Return - May not be ground, but a differential voltage return.
Sensor Signal = Signal used to provide pedal distance converted into voltage

The only useful wire in this diagram is the Sensor Signal.

Pin 3 would be the output from the potentiometer. If you put your relay in-line between 3 and 23, you will tell the brake module that the pedal has been pressed.

As long as that relay is providing the right input expected. This is the part I don't know. I'm not sure what that signal should look like. I would have to test/scope it myself.
 
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These are the installation instructions for the relay.

Installing the Brake Circuit Disconnect..........

Step 1. Locate the brake light switch. This switch is generally found toward the uppermost part of the brake pedal arm. Refer to owners manual or seek the advice of a technician if you have problems finding this switch.

Step 2. Locate the wire that sends a signal to your brake lights from this switch. There will be two wires running to this switch. One supplies the switch with a constant 12 volt current, the other sends this current to the tail lights when the brake is activated. The wire which carries the signal to the brake lights upon activation of the brake pedal is the wire you will run to the relay.

Step 3. Cut the wire located in step 2. Make sure to cut the wire that carries the signal to the brake light located in step 2. Leave enough length to splice it to the wires coming from the relay. The relay can then be wire tied or permanently mounted under the dash to a suitable structure.
 
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This is also from the instructions - I'm not plugging mine into the cigarette lighter as it's not powered when the JL is shut off. I'm running a power lead to the tow harness wiring and pulling 12v off the motorhome to power the relay. I don't want the Jeep's battery powering the relay if we're driving 8 or 10 hours as I don't know how much power the relay will pull out of the battery.
Screen Shot 2020-10-21 at 5.36.37 PM.png
 

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Skip,

B137 is the wire you need.

BUT

B137 is going to be a variable voltage whereas your instructions are expecting full battery voltage (12vdc)

Do you have a diagram or can you tell me where the Dark Blue wire above is going on the relay? Is it to X1 or X2?
 


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Skip,

B137 is the wire you need.

BUT

B137 is going to be a variable voltage whereas your instructions are expecting full battery voltage (12vdc)

Do you have a diagram or can you tell me where the Dark Blue wire above is going on the relay? Is it to X1 or X2?
The dark blue wire is going to position 30 on the relay. The power in/power out go to 85 and 86, the light blue wire is attached at 87a
 

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Alrighty.

It makes a little more sense now.

With the plug unplugged, the relay goes to a normally closed state as if you never cut the wire.

You can use B137. That is the right wire.
 

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The dark blue wire is going to position 30 on the relay. The power in/power out go to 85 and 86, the light blue wire is attached at 87a
Here is a little diagram of a standard relay if you should ever need it.

Yours is requiring it to be connected in a N/C (Normally Closed) state.

This means as long as the coil is dead, it is wired to allow the load through.

1603317856021.png
 


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Here is a little diagram of a standard relay if you should ever need it.

Yours is requiring it to be connected in a N/C (Normally Closed) state.

This means as long as the coil is dead, it is wired to allow the load through.

1603317856021.png
Thank you sir! You just made my life a lot easier. This one got confusing for me because it's backwards from how my JK was set up. I bought the Brake Circuit Disconnect from the company that makes the tow bar (Readybrute). When I put it on the JK that I had the relay was setup for normally open. I sold the JK with it installed and just got the new one for the JL. In order for the JK's brake lights to work I had to have the power for the relay tied to an ignition source so that the relay was powered when the JK was running. This one threw me as it is just the opposite where it needs to be powered when the JL is shut off. I miss the old days when you had a positive and a negative wire for everything, set the points with a matchbook and the timing with a strobe light....ah, the good old days!
 

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This is definitely not a CAN bus. It's a potentiometer.
I know the difference between a CAN bus and a potentiometer thank you very much. What I'm getting at is that that ABS module IS on the CAN bus and that switch is probably monitored by the CAN bus. It's probably not even a 0-12 volt signal going across that potentiometer, impossible to know without seeing what is coming out of the ABS module. I think hacking that relay in there is going to cause problems. Once again without seeing what happens in the module it's a guessing game, I hope it does work for the OP.
 
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I know the difference between a CAN bus and a potentiometer thank you very much. What I'm getting at is that that ABS module IS on the CAN bus and that switch is probably monitored by the CAN bus. It's probably not even a 0-12 volt signal going across that potentiometer, impossible to know without seeing what is coming out of the ABS module. I think hacking that relay in there is going to cause problems. Once again without seeing what happens in the module it's a guessing game, I hope it does work for the OP.
I had basically the same setup on my JK and it worked fine. Basically the relay is just an on/off switch for the line coming out of the brake switch. When it's not powered it's in the closed position so the CAN bus shouldn't even see the relay there as the relay is just a passthrough for the signal. When the relay is open/working the Jeep is not going to be running so the CAN bus won't have anything to do with it at that point. I'm going to power the relay from the 12v power feed off the motorhome's umbilical cord.
I understand your concern and thank you for that.
 

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I think the issue is your install instructions are expecting a brake switch sensor (just to turn on lights) not a pedal travel sensor (for controlling the electronic anti-lock brakes).

If it were me, I wouldn't splice into the pedal travel wire, you're going to be adding additional resistance to the signal which could cause issue with the anti-lock brakes.

If I understand correctly, this is just to ensure the motorhome wiring can always control the brake lights? if so, I think a safer bet would be to splice wire B15 (BRAKE SIGNAL 1) where the Anti-lock Brake module sends the signal to the BCM

https://www.jlwranglerforums.com/JL-Wiring-Diagrams/STOP-LAMPS-SYSTEM.pdf
 
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Captain Skip

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I think the issue is your install instructions are expecting a brake switch sensor (just to turn on lights) not a pedal travel sensor (for controlling the electronic anti-lock brakes).

If it were me, I wouldn't splice into the pedal travel wire, you're going to be adding additional resistance to the signal which could cause issue with the anti-lock brakes.

If I understand correctly, this is just to ensure the motorhome wiring can always control the brake lights? if so, I think a safer bet would be to splice wire B15 (BRAKE SIGNAL 1) where the Anti-lock Brake module sends the signal to the BCM

https://www.jlwranglerforums.com/JL-Wiring-Diagrams/STOP-LAMPS-SYSTEM.pdf
OK, did I post the wrong wiring diagram then? I'll look at all the available wiring colors on the switch before I start cutting anything. I do remember that when I did it on the JK (2015) it worked fine and didn't have any issues with the ABS....they worked when I slammed on the brakes!

 

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