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Old 07-25-2015, 06:00 PM   #1
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Toad Brake Feedback - Why do I care?

Ok, calling all you 12v electrical experts. So I bought a Grand Cherokee this year and wired it up for towing behind the coach. With the GC, when depressing the brake pedal it will feedback to the coach and the coach brake lights will come on. This doesn't happen with my Miata or the TJ so I've never had to consider this in the past. I do have a relay available that I can wire into the GC brake pedal to disconnect the circuit when it is being towed but the new vehicles are so tight and sealed up under the footwell that I really don't have a lot of ambition to attempt to get in there and wire it.

From a day to day driving perspective, I am pretty proactive so it is fairly rare that I brake hard enough to trigger the auxiliary brake on the toad. Can someone tell me whether I should care that I have 12v feeding back into the coach on rare occasion and why I should care?
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Old 07-25-2015, 06:18 PM   #2
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We just had our CRV set up with Invisabrake. It has a feedback circuit that lights a indicator they installed on the dash to let you know the toad brakes are activating. If you are at a stop light for a while, the road brakes automatically disengage and the light goes out, saving battery usage in the toad.

I don't know if it also turns on the MH brake lights.
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Old 07-25-2015, 06:50 PM   #3
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If depressing the brake pedal on the GC is making the motor home brake lights come on you have a shorted diode in your diode pack (or two) or the pack is not properly installed. It is that simple.

Unless of course some idiot shorted the MOTOR HOME and JEEP lines together (Doubtful)
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Old 07-25-2015, 10:35 PM   #4
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Quote:
Originally Posted by MandG-Fun View Post
Ok, calling all you 12v electrical experts. So I bought a Grand Cherokee this year and wired it up for towing behind the coach. With the GC, when depressing the brake pedal it will feedback to the coach and the coach brake lights will come on. This doesn't happen with my Miata or the TJ so I've never had to consider this in the past. I do have a relay available that I can wire into the GC brake pedal to disconnect the circuit when it is being towed but the new vehicles are so tight and sealed up under the footwell that I really don't have a lot of ambition to attempt to get in there and wire it.

From a day to day driving perspective, I am pretty proactive so it is fairly rare that I brake hard enough to trigger the auxiliary brake on the toad. Can someone tell me whether I should care that I have 12v feeding back into the coach on rare occasion and why I should care?
ManG-fun,
Well Sir, the actual feed back of the brake light signal from your GC to your coach, may or may not have any detrimental effects, depending on just what's happening in the circuits at the time. That is, if all you're doing is braking, then you'll have brake lights on the coach, from the coaches sending unit and, you'll have feed back from the GC also feeding the same filaments in the coach and the GC. In all reality, no biggie.

But, where it get's complicated is when a turn signal is applied to either side. Then things can go south in a hurry. I have a question for you though. You say your "TJ" didn't or, does not provide feedback from the same brake application? To me, that's kind-a odd. We towed an '04 Jeep Rubicon and, as with many toads, the brake light switch on the TJ, activated the Jeeps brake lights, when the Ready Brake auxiliary braking system I was using at the time, applied pressure on the Jeeps brake pedal.

And as with many toads out there, that will happen even with the ignition key, completely out of the vehicle. The '04 TJ needed the key to be turned one click to un lock the steering but, didn't trigger any electrical operation like ignition or, any other 12V power problems.

Now, my remedy for this was simple to me. I simply installed a small two way toggle switch in the door jamb of the TJ. I then cut the output wire from the Jeeps brake light switch, and sent it up to the center post on that toggle. I then sent a wire from one side of that toggle, all the way to the dash on the coach, and wired in a small LED light. I then ran another wire from the other side of that little toggle, back to the Jeeps out put wire where I cut it in the first place.

Now, when towing, we flip that switch and, the jeeps brake light signal is sent to the dash of the coach and, lights up the LED, indicating that the Ready Brake is doing its job. But, when driving that Jeep, we flipped that switch the other way and, that sent the Jeeps brake light signal to the Jeeps tail lights, just like it should.

Now, that took care of the problem of the toad activating the brake lights via an auxiliary brake, especially since I was using the Jeeps tail lights as toad lights when towing. I'm not a fan of adding additional bulbs and sockets.

Now, that brings me to the infamous "diodes". I install my own style of diodes in the line, just south of each of the Jeeps (and any other toad I've towed over the years) tail lights. That prevents back feeding of the coaches signals into parts of the Jeeps wiring, where it's not supposed to go.

If you really want to stop the back feeding of that GC brake light signal from entering the coaches wiring, just install some cheap, Radio Shack high amp diodes, one in each signal wire, from the coach, to prevent that back feeding from entering the coaches wiring system, where it's not supposed to go in the first place. Good luck.
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Old 07-26-2015, 07:46 AM   #5
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Thanks for sharing your interesting solution to controlling the circuit and having a tell-tale light to know when the aux brake is being applied.

Here's a little more detail. On both my Miata and TJ I took the cheap route, not wanting to spend a bunch of $'s on stupid diodes. The GC is a '15 and considering the complexity of the electronics on this vehicle I decided to blow even more money than this luxo-4-wheeler cost and I saw that TrailerMate builds a vehicle-specific harness with integrated diodes. No cutting wires, just pop out the tail lights unplug the cable, plug in the harness, plug the cable into the TM harness and just route the cables to the front.

Having not owned a vehicle newer than an '02 previously, the GC is all new territory. First there is no key... when flat towing you start the engine, place the tranny in neutral, depress a small button for shifting the T-case into neutral, hold the start button for a few seconds to shut off the engine then give the shifter a push forward to put the tranny in park. The computer takes care of everything else, no turning a key to unlock the steering wheel or anything else, it just knows you're flat towing and life is good.

When I am hooking up to the coach and step on the brake in the GC the coach brake lights come on. There is no issue with the turn signals, when we do our light check of turns and brakes from the coach everything works properly on the GC and the coach tail lights. I use an RVi aux brake so I have a remote display up front to see when it is applying the brakes. From the RVi remote I can activate the aux brake unit. I've run a test and had my wife look at the coach and GC tail lights and I depressed the coach brake and activated the RVi remote simultaneously. Didn't see any problem with the brake lights on either vehicle.

On the occasions when I am braking hard and the aux brake is activated too, the coach is sending power to the coach tail lights and the GC... and the GC is sending power to both as well. So I'm really just curious if there is anything detrimental that I am not aware of...
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Old 07-26-2015, 09:35 AM   #6
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Quote:
Originally Posted by MandG-Fun View Post
not wanting to spend a bunch of $'s on stupid diodes.
It's the stupid diodes that would prevent this problem.

Quote:
I saw that TrailerMate builds a vehicle-specific harness with integrated diodes. No cutting wires, just pop out the tail lights unplug the cable, plug in the harness, plug the cable into the TM harness and just route the cables to the front.
That harness should have the diodes built into it, yet you are still getting feedback? You should not be getting feedback with such a harness. There are a few possible reasons:
  • Improperly designed harness
  • Defective harness
  • Incorrect installation

Quote:
There is no issue with the turn signals, when we do our light check of turns and brakes from the coach everything works properly on the GC and the coach tail lights.
That may be true in normal cases. However, what happens when the toad's brakes are active and you have that feedback?

If the coach is braking, the brakes lights will be on, and both systems are driving the circuit. That may or may not cause a problem, probably not.

But things get interesting when the turn signal is on, and the toad brakes are applied:
  • The motorhome signal will periodically turn off as the light flashes. At that point, the toad is back-feeding the turn signal circuit. Things could get interesting depending on how the coach is wired.
  • The turn signal will try to flash the toad light, but the brake signal will override it to be on steady. But if the toad is back-feeding the circuit, it could end up lighting the motorhome tail light as well. People behind you may have no idea that the turn signal is on.

An additional concern is if that harness, which should not allow backfeeding, is indeed allowing the toad to backfeed the motorhome, is it also allowing the motorhome to backfeed the toad's circuits? That is generally not a good idea, especially in these days of sophisticated car electronics driving things. You don't want to end up burning out an expensive body control computer.

You can run all of the tests you want, and convince yourself that you don't have a problem. But as long as you are backfeeding the motorhome, you have a problem, and without knowing exactly what that problem is, you don't really know the consequences of it. The harness you are using should not be doing what it's doing, what other incorrect things might it be doing?

I think you have two issues:
  1. The toad is backfeeding the motorhome
  2. The toad brake pedal is driving the tail lights, which could override a turn signal.
Problem 1 is probably being caused by the harness and the solution will be in there.

Problem 2 is often solved by the addition of a switch, or a relay. My brake system has an electric vacuum pump to build brake boost pressure - I tapped a relay into that signal so the relay is active whenever the brake system is actively braking (and for about 20 seconds after that.) When the relay comes on, it breaks the toad's brake switch circuit.
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Old 07-26-2015, 02:12 PM   #7
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Yep I 2nd what Adam said!
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Old 07-26-2015, 03:27 PM   #8
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If you get the diodes right, you will solve the backfeed issue. However, I didn't want to crawl under the dash and start cutting wires from the brake switch, either. You would need a small child with 3 arms to get to mine. On the rare occasion when I hit the brakes hard enough to activate the toad's brakes, it may briefly overide the turn signal on the toad. I usually anticipate my turns well in advance. I find that acceptable. YMMV
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Old 07-26-2015, 05:10 PM   #9
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Oh there is another solution. this is a trade marked name but very descriptive "Add a lamp"

In this system a hole is drilled in the side of the tail light housing and a 2nd tail light (1157 or the blade equivlent) is "Snapped" in That way the tow lights and the vehicle service brake/tail/turn lights are independent, Nothing common except OPTIONALLY the chassis ground (On mine that is not even common)

That is how my car is wired.
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Old 07-26-2015, 05:16 PM   #10
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Oh there is another solution. this is a trade marked name but very descriptive "Add a lamp"

In this system a hole is drilled in the side of the tail light housing and a 2nd tail light (1157 or the blade equivlent) is "Snapped" in That way the tow lights and the vehicle service brake/tail/turn lights are independent, Nothing common except OPTIONALLY the chassis ground (On mine that is not even common)

That is how my car is wired.
The only problem if you have a toad braking system (except the M&G ) that mashes the toad brake it will cover up the turn signal. Like you I really hate to cut into my system.
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Old 07-26-2015, 06:55 PM   #11
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The only problem if you have a toad braking system (except the M&G ) that mashes the toad brake it will cover up the turn signal. Like you I really hate to cut into my system.
And if you have a truly proportional system (as opposed to an inertial system set to only activate on hard braking) then the toad brakes are likely to be applied on every MH service brake application.

I also hate cutting into a factory system, but sometimes it needs to be done. An alternative is to find the fuse that feeds the brake switch, and either pull the fuse every time, or replace the fuse with a special harness: there are several, HERE IS ONE.
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Old 07-26-2015, 08:39 PM   #12
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I also hate cutting into a factory system, but sometimes it needs to be done. An alternative is to find the fuse that feeds the brake switch, and either pull the fuse every time, or replace the fuse with a special harness: there are several, HERE IS ONE.[/QUOTE]

That is a good idea Adam and looks pretty easy to build for just a few bucks but I went another route on both of my toads I used a 48 inch led tail, stop, signal light strip attached to the bottom lip of the tailgate and LED lights installed in place of the false tail lights in the bumper of the Kia.
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Old 07-28-2015, 02:01 PM   #13
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It's the stupid diodes that would prevent this problem.
I did a poor job of explaining myself here... I did use diodes in my wiring of the Miata and TJ, just purchased cheap ones at Radio Shack and soldered them inline as opposed to spending a lot of money on fancy ("stupid") diodes made for vehicle towing. This setup works perfectly with those two vehicles, no brake light feedback.


Quote:
Originally Posted by ShapeShifter View Post
That harness should have the diodes built into it, yet you are still getting feedback? You should not be getting feedback with such a harness. There are a few possible reasons:
  • Improperly designed harness
  • Defective harness
  • Incorrect installation


That may be true in normal cases. However, what happens when the toad's brakes are active and you have that feedback?

If the coach is braking, the brakes lights will be on, and both systems are driving the circuit. That may or may not cause a problem, probably not.
I've tested brakes and turn signals and the only abnormal behavior is the brake feedback to the coach brake lights. The turn signals do not cause any strange light behavior with and with the brakes applied.

Perhaps the harness is defective. Considering the effort that I went through to cleanly bury and protect the cabling from the rear to the front I am not too motivated to uninstall it and install a new harness. At this point I'm thinking the best course of action may be to just install my own diodes into the wiring.
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Old 07-28-2015, 02:41 PM   #14
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I did a poor job of explaining myself here...
Thanks for the clarification, that makes a lot more sense. I did indeed read it incorrectly.

Quote:
At this point I'm thinking the best course of action may be to just install my own diodes into the wiring.
Installing a pair of diodes in the aftermarket harness between the umbilical connector and the lighting sounds like a reasonable solution, as long as the motorhome signal isn't backfeeding the Jeep. Is a third diode needed for the running lights? I'd be more concerned about the Jeep, as it's more likely to have sensitive electronics driving the lights, where the motorhome is more likely to have relays.
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