Stop Engine Brake from Turning on Brake Lights

[BonS]

There are times when I'd like to not have the engine brake not turn on the brake lights. My toad braking system is activated by the brake lights and when driving in rolling hills and on cruise control the engine brake constantly cycles my toad brakes. I can see the activation on my dash monitor and they're on a lot more, and longer, than I like. On the other hand, there are times when having the engine brake and service brake both coupled together. As I understand it, some coach makers tie the two together and others don't. This thinking has led me to examine how CC ties the two together and how I can tweak the circuitry to make it work as I want. I'm leaning toward adding a switch on my left side to select this option.

With that introduction, I'll present what I have learned. In the earlier years, CC used a single relay and two diodes to combine the engine brake signal, which comes from the engine control module (ECM) and the service brake signal that comes from the service brake switch. The first image shows the "Double Diode Method" as I call it. The engine brake signal and the service brake signal both feed in to the same relay "Brake Light Relay". Each signal wire has a series diode. The diodes keep the two inputs separate so that the engine brake doesn't cancel the cruise control, for instance. As far as I know, all CC's used this circuit until near their last year of production.


To separate brake lights from the engine brake and service brake then a single cut of wire #1148 does it. A switch can be added to allow the circuits to be recombined as desired. The Brake Light Relay and double diodes are found in the front run bay.


My '09 CC did away with the double diode approach and instead used a double relay and no diodes. The reason for the circuit change is reduced labor. The double relay circuit has a "Brake Light Relay" as well as a "Engine Brake Load Relay".

To separate brake lights from the engine brake and service brake then a single cut at the "X" does it. A switch can be added to allow the two circuits to be recombined as desired. The Brake Light Relay and Engine Brake Load Relay are found in the front run bay. The wire marked "JUMP" is found behind the cluster of Bussman fuses, relays, and diodes mounted on the inboard wall of the front run bay. If simply stopping the engine brake from activating the brake lights is the goal then simply removing the Engine Brake Load Relay will accomplish that goal.

Now that I have decoded the wiring logic, next week I will be testing how my double relay modification works. I'll be testing the results of simply cutting the jumper wire between the relays as well as pulling the Engine Brake Load Relay without cutting the jumper. I will follow up with results. I don't have a double-diode system to test so I'll leave that to others.

[CountryFit]

Interesting topic... On my old Intrigue the exhaust brake doesn't turn on the brake lights unless I step on the service brake. Did CC change the design on the later year coaches?

[Old-Biscuit]

Check out the discussion on that topic.
Might want to chime in there

https://www.irv2.com/forums/f278/eng...se-585949.html

[BonS]

Originally Posted by CountryFit

Interesting topic... On my old Intrigue the exhaust brake doesn't turn on the brake lights unless I step on the service brake. Did CC change the design on the later year coaches?

I certainly don't know the entire CC history of this, but I've worked from an '08 Magna schematic for the double diode method and I've decoded my '09 double relay wiring manually because CC didn't document it as well as previous coaches. I'd love to see some other schematics of earlier coaches to see if there are any other variations. I suspect that their either independent like yours or joined by the double diode method.

[BonS]

Originally Posted by Old-Biscuit

Check out the discussion on that topic.
Might want to chime in there

https://www.irv2.com/forums/f278/eng...se-585949.html

Thanks for that. I read through it and I'm not sure that I want to get into that brouhaha. I understand why I want to do this and that's all I'm doing. There are a lot of intricacies when it comes to trailers, toads and brakes that makes for a confusing general discussion of this issue. In my specific case I want the choice so I can implement my driving/braking strategy based upon the circumstances on hand.

[Smitty77]

This is a non specific coach conversation. And IMO, anytime you have a 'slowing influence' to the coach... It is certainly safer to communicate to someone behind you, with brake lights.

That being said, none of the vast population of three coaches/RV's we've had, have activated the Brake Lights when either Jake, or Downshifts of the transmission, have occurred...

A general comment that I feel is sound: If possible, OVER COMMUNICATE, to those behind you, of slowing conditions!

Smitty

[BonS]

Hi Smitty, I understand your perspective and intent. And agree in many cases. That said, I'm concerned with specific use cases where I, and folks in front and back of me, could be very happy with my choices. One example is when going downhill and my engine brake is on, but not my service brake, the Invisibrake in my toad automatically turns off after 30 seconds so no toad brakes at all. I would rather use just my engine brake for downhill speed control and save my toad brakes for when I am needing more serious braking - and not have the toad brakes not working because of that timeout or possible overheating. If using the engine brake while slowing for a stop I can always put a little toe into the service brake to activate the brake lights as usual. Or - just flip a switch to tie them back together when desired. Other times, the engine brake comes on during a downhill stretch due to the cruise control retarding my excess downhill speed. I can use low or high engine brake to manage my energy just to avoid over speeding. I can't imagine that a trailing car needs to be warned that I'm not speeding down a hill, but I am saving my toad brakes for when I need them while using my service brakes.

[NowGo]

Originally Posted by BonS

Thanks for that. I read through it and I'm not sure that I want to get into that brouhaha. I understand why I want to do this and that's all I'm doing. There are a lot of intricacies when it comes to trailers, toads and brakes that makes for a confusing general discussion of this issue. In my specific case I want the choice so I can implement my driving/braking strategy based upon the circumstances on hand.

Thank you for your post and for the diagrams. I am the OP from the link Old Biscuit provided. I tried to keep the thread to technical information, but I was unsuccessful.

I have a 2014 Entegra Anthem and I am trying to determine what applies to my specific coach. All of this information helps. Thanks again.

As a result of the debate that ensued from my original post I will be posting my logic for the desired mod, not to fuel debate, but just in case some of what I have to say might be valuable. I end the post by quoting part of your last sentence "I want the choice so I can implement my driving/braking strategy based upon the circumstances on hand"

[BonS]

Thanks for joining the discussion, NowGo. I would love to see any schematics that you have showing your engine/service brake wiring. Also, I may be able to offer something other than the all-or-nothing approach to this issue. What I mean is an alternative wiring option that turns on the coach brake lights but doesn't turn on the toad/trailer brake lights when just the engine brake is in use. The service brakes would always turn on both. In any case I don't see any reason to reprogram the ECM to make this happen.

[NowGo]

Originally Posted by BonS

Thanks for joining the discussion, NowGo. I would love to see any schematics that you have showing your engine/service brake wiring. Also, I may be able to offer something other than the all-or-nothing approach to this issue. What I mean is an alternative wiring option that turns on the coach brake lights but doesn't turn on the toad/trailer brake lights when just the engine brake is in use. The service brakes would always turn on both. In any case I don't see any reason to reprogram the ECM to make this happen.

Thanks BonS
I have attached the schematic for my trailer brake controller as well as a schematic I created that will defeat the activation of the trailer brakes by the engine brake.
However, this doe not deal with the issue of the engine brake defeating the hazard lights when moving (such as when descending a hill with the hazards on). If you like I have posted my "dissertation" on page 48 of https://www.irv2.com/forums/f278/eng...-585949-4.html

I am hoping to deal with BOTH the trailer brake activation and the hazard light issue with the same mod... namely no activation of stop/brake lights by the engine brake. I do however like the idea of making it switchable. If I have to settle for dealing with the trailer brakes only I will use my proposed mod as per these schematics, but I am hopeful I can "kill two birds with one stone"

[Smitty77]

Originally Posted by BonS

Hi Smitty, I understand your perspective and intent. And agree in many cases. That said, I'm concerned with specific use cases where I, and folks in front and back of me, could be very happy with my choices. One example is when going downhill and my engine brake is on, but not my service brake, the Invisibrake in my toad automatically turns off after 30 seconds so no toad brakes at all. I would rather use just my engine brake for downhill speed control and save my toad brakes for when I am needing more serious braking - and not have the toad brakes not working because of that timeout or possible overheating. If using the engine brake while slowing for a stop I can always put a little toe into the service brake to activate the brake lights as usual. Or - just flip a switch to tie them back together when desired. Other times, the engine brake comes on during a downhill stretch due to the cruise control retarding my excess downhill speed. I can use low or high engine brake to manage my energy just to avoid over speeding. I can't imagine that a trailing car needs to be warned that I'm not speeding down a hill, but I am saving my toad brakes for when I need them while using my service brakes.

Completely understand what you're trying to do, have a good friend with a Dutch Star and a new Toad that came with the Invisibrake, and is researching hot disable the brake application too... And to show I'm a bit hypocritical in my earlier post... I do have my Allison ECM Jake Default gear set to 6th gear, and our Cummins ECM set to 3 MPH over set Cruise Speed, to activate the Jake. (I travel on the highways in Stage 2, and find that typically will bring me down again to the set speed on gradual up/downs of the highway relatively quickly! I manually downshift as needed, and go Stage 1 and Stage 3 as needed. Especially on long steep downgrades...) And, my Brake Lights do not come on when Jake is activated. So I manually will tap my brakes if I feel my Jake's slowing is more then just the gradual dropping back down to set cruise speed. Then hit Resume when I'm at desired speed. ---- So I admit that what I typed, I manually control, as far as communicating to those behind me about 'slowing'!

My comment was more in general, and not targeted at what you're doing - I was not clear in my post... Hope the schematics help!!

Smitty

[palehorse89]

Originally Posted by NowGo

Thanks BonS
I have attached the schematic for my trailer brake controller as well as a schematic I created that will defeat the activation of the trailer brakes by the engine brake.
However, this doe not deal with the issue of the engine brake defeating the hazard lights when moving (such as when descending a hill with the hazards on). If you like I have posted my "dissertation" on page 48 of https://www.irv2.com/forums/f278/eng...-585949-4.html

I am hoping to deal with BOTH the trailer brake activation and the hazard light issue with the same mod... namely no activation of stop/brake lights by the engine brake. I do however like the idea of making it switchable. If I have to settle for dealing with the trailer brakes only I will use my proposed mod as per these schematics, but I am hopeful I can "kill two birds with one stone"

I might be missing it , but I don't see your engine brake in the diagram. The brake light activation gets a signal from the engine brake when in use.....
Following both your thread's!

[BonS]

From your provided Spartan schematic it appears that all logic is contained in the Spartan Control Module. This may be the limiting factor to your flexibility. There is nothing in the schematic about your engine brake circuitry and that is essential to designing a good workaround.

The output of the Spartan Control Module, as shown here, doesn't allow you to differentiate between engine braking and service brake. If all you wanted to do is to interrupt the brake signal to your trailer then you have identified the correct place to insert a relay or switch to interrupt the signal. That said, the #86 terminal needs to go to 12 Volts and not ground.

[NowGo]

Originally Posted by palehorse89

I might be missing it , but I don't see your engine brake in the diagram. The brake light activation gets a signal from the engine brake when in use.....
Following both your thread's!

The SCM sends signal to the brake controller using AP1081A. The source of the signal TO the SCM is not shown.

This is one of the fundamental issues I am trying to deal with as I try to also deal with engine brake also deactivating the hazards (Stop/brake lights go to steady on when engine brake is activated).

Specifically, how/where does the ECM send signal to the SCM, and if I disable that what else might be impacted? For instance, the engine brake disables the cruise, and I certainly don't want to mess with that.

By original design the SCM sends signal to the brake controller using AP1081A. Once the controller gets signal from the SCM via SP1018A (due to engine brake activation OR the the stop pressure brake switch), it determines the inertia and applies brakes (as best it can).

By limiting the signal the controller receives to that provided by the stop pressure brake switches and NOT the SCM (SP1018A) the controller will only provide braking when the service brakes are used. The brake controller WILL provide stop/brake lights to the trailer (SP1018B), but will not provide braking power (SP709B) unless you apply the service brakes. Deals with the trailer brake issue, but not the coach and the hazard lights.

It may be that the SCM programming is the ONLY way to deal with this, as Gary Jones has suggested. I hope not. In that case I do not know what options exist in the programming, and I will need to find someone to do it. I do believe some of the newer trucks (e.g. Kenworth, etc.) are coming with this same issue, and the owner/operators are very promptly taking their trucks in to have this dealt with, but I don't know what options area available in the programming.

I do not want the engine brake in latch mode as programmed in ECM (requires application of the brake pedal to trigger the engine brake). I ONLY want to have the the engine brake stop from turning the stop/brake lights on.
Hope that makes sense