Stop Engine Brake from Turning on Brake Lights

[BonS]

Okay, NowGo, I think I have a candidate solution for your Spartan chassis. I've made changes to your PDF and it's linked here. I modified your relay wiring to activate the relay when the chassis service brake is grounded through the two service pressure switches. (I'd love to know why two switches in series but it is what it is.) The relay coil + needs 12 volts while the coil - is supplied by the service brake switches. The relay N.O. contact bridges the cut brake light wire. So, if the service brake is not active then the brake lights do not turn on. The engine brake is free to operate without activating the brake lights. To address your hazard lights you'll need a second relay or switch. A switch can simply bridge the cut circuit. A relay can be activated by the 12 volts at the hazard switch and bridge the cut circuit. I like the second relay solution as its automatic. When the hazards are on then your brake lights will perform however Spartan designed them. Some OEM's prioritize hazards over brake lights and others do not.

Spartan Trailer brake with relay.pdf

Finally, I would add a relay flyback diode to protect the SCM. If you have any questions about that let me know.

Comments? Questions?

[BonS]

Originally Posted by Smitty77

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

You've got a really nice setup there. The description of your setup, and insights are gold and always appreciated.

[NowGo]

Originally Posted by BonS

Okay, NowGo, I think I have a candidate solution for your Spartan chassis. I've made changes to your PDF and it's linked here. I modified your relay wiring to activate the relay when the chassis service brake is grounded through the two service pressure switches. (I'd love to know why two switches in series but it is what it is.) The relay coil + needs 12 volts while the coil - is supplied by the service brake switches. The relay N.O. contact bridges the cut brake light wire. So, if the service brake is not active then the brake lights do not turn on. The engine brake is free to operate without activating the brake lights. To address your hazard lights you'll need a second relay or switch. A switch can simply bridge the cut circuit. A relay can be activated by the 12 volts at the hazard switch and bridge the cut circuit. I like the second relay solution as its automatic. When the hazards are on then your brake lights will perform however Spartan designed them. Some OEM's prioritize hazards over brake lights and others do not.

Attachment 370021

Finally, I would add a relay flyback diode to protect the SCM. If you have any questions about that let me know.

Comments? Questions?

Thank you for your work on this BonS.

Well, now I am confused. Maybe I am interpreting the Spartan schematic incorrectly. In the original Spartan design I saw SP1018A as supplying + directly to the brake controller when the brake lights are on My design interrupted that by installing a relay that would be activated by taking the + signal from the downstream of the brake pressure switches (SP 185L connected to 85), and grounding it to complete the circuit (this is why I had 86 to ground). This only has effect when both brake pressure switches are closed, since there will be no + at 85 unless they are closed. In other words, this only happens when when the + signal from the SCM SP1096A arrives at the downstream side of the brake pressure switches on SP185L, using it to operate the relay by connecting it to 85. When the brake pressure switches are closed, the + signal from SP185L goes to ground though the relay. This would activate the relay, and the coil side of the relay would close the SP1081A circuit, passing + to the brake controller, therefore activating the trailer brakes.

The way I interpret your schematic, 12v is supplied to SP1096A, potentially back feeding the SCM. When the brake pressure switches are closed, the circuit is closed to ground, and this activates the relay. This looks like the same effect as my design, but with the risk of back feeding the SCM?

What am I missing ?

However, either way this still only deals with the trailer brake issue, and not the hazard light issue.

[BonS]

Well, now I am confused. Maybe I am interpreting the Spartan schematic incorrectly. In the original Spartan design I saw SP1018A as supplying + directly to the brake controller when the brake lights are on. SP1018A supplies a 12-volt signal to 64C the “customer supplied electronic brake controller”. This device usually draws the power for the run/brake/turns from the 12-volt supply SP900A as it is fused @ 30 amps.

My design interrupted that by installing a relay that would be activated by taking the + signal from the downstream of the brake pressure switches (SP 185L connected to 85), and grounding it to complete the circuit (this is why I had 86 to ground). The point where you show 85 connecting is always connected to chassis ground. Line A, SP185L, is always connected to SPL-19 chassis ground. Relay connection 85 needs +12V to turn on and 86 must see ground.

This only has effect when both brake pressure switches are closed, since there will be no + at 85 unless they are closed. In other words, this only happens when the + signal from the SCM SP1096A arrives at the downstream side of the brake pressure switches on SP185L, using it to operate the relay by connecting it to 85. When the brake pressure switches are closed, the + signal from SP185L goes to ground though the relay. This would activate the relay, and the coil side of the relay would close the SP1081A circuit, passing + to the brake controller, therefore activating the trailer brakes. Since SP185L is always connected to chassis ground this won’t work. It is for this reason that I moved the relay activation connection to A, SP1096A. This is the point that goes high (12V) or low (ground) depending upon the status of the service brake pressure switches.

The way I interpret your schematic, 12v is supplied to SP1096A, potentially back feeding the SCM. When the brake pressure switches are closed, the circuit is closed to ground, and this activates the relay. This looks like the same effect as my design, but with the risk of back feeding the SCM? The connection to 85 (the coil -) is grounded through the brake switches to chassis ground at SPL-10. When the switches are opened then 85 floats to 12V provided by 12V on 86 and the pull up resistor internal to the SCM, shown as internal at B2. In other words the relay turns off. Floating up to 12V when the switches are open is a normal event in the OEM design, so it is not a threat to the SCM. I mentioned adding a flyback diode to the coil of the relay as an extra precaution to the SCM to avoid exceeding 12V that can occur due to the relay coil turning on and off. This is a typical precaution and a wise one.

What am I missing?
Hopefully, this is getting clearer. If not, I’ll add additional notes to your schematic that will help. We can talk by phone if you’d like. PM me and we can exchange info.

Post note:
After examining the schematic - again, I believe that the brake pressure switches are “normally closed” when the service brake is inactive (off). If that is the case, then use the normally closed contact 87A instead of the normally open contact 87. However, either way this still only deals with the trailer brake issue, and not the hazard light issue. Let’s get to a clear understanding of brake light operation and then we can circle back around to the hazards as they’re easy.

[palehorse89]

Good morning Gentleman, Happy 4th to all you!
Been trying to defeat this problem also, now I have a question, I run the Prodigy wireless brake controller, so the brain center is on the trailer and a small display/controller just plugs into a 12v dash outlet. But this part of the controller is paired with the brake pedal operation in the setup.
So with this setup how would I deal with the engine brake logic in the SCM turning on my brake lights? found this on the Tiffin forum the other day, but not sure in the explanation of the connection point's.......
I do have a 2 position engine brake on a 500 ISX

[palehorse89]

Looking at a print this morning I also see that the VGT is wired into this circuit also....But I can't get the file on here as it is to big and I can't find a way to just separate that page to post it..........
Thinking now for me any change would have to be on the output of the SCM......?

[palehorse89]

Originally Posted by palehorse89

Looking at a print this morning I also see that the VGT is wired into this circuit also....But I can't get the file on here as it is to big and I can't find a way to just separate that page to post it..........
Thinking now for me any change would have to be on the output of the SCM......?

That won't work either.......brain if fogged on this subject?

[BonS]

Good morning palehorse89. I'm not familiar with the Prodigy brake controller, but your description is clear. The PDF you attached shows a wiring scheme that serves the purpose of turning on the brake controller if you are just using the engine brake or the service brake, but it does not attempt to change the brake light logic in any way. Is that correct?

The Spartan schematic that we're referencing might/should apply to your coach. Have you given it a look and does it look like yours?

The approach we're discussing doesn't get involved with the engine Hi/Lo switch or PURPLE wire engine brake signal in any way so your Prodigy will work as normal if the modification discussed is accomplished.

[gpounder]

I believe this is programable as part of the CANN under the engine or transmission.

[NowGo]

Originally Posted by BonS

Well, now I am confused. Maybe I am interpreting the Spartan schematic incorrectly. In the original Spartan design I saw SP1018A as supplying + directly to the brake controller when the brake lights are on. SP1018A supplies a 12-volt signal to 64C the “customer supplied electronic brake controller”. This device usually draws the power for the run/brake/turns from the 12-volt supply SP900A as it is fused @ 30 amps.

My design interrupted that by installing a relay that would be activated by taking the + signal from the downstream of the brake pressure switches (SP 185L connected to 85), and grounding it to complete the circuit (this is why I had 86 to ground). The point where you show 85 connecting is always connected to chassis ground. Line A, SP185L, is always connected to SPL-19 chassis ground. Relay connection 85 needs +12V to turn on and 86 must see ground.

This only has effect when both brake pressure switches are closed, since there will be no + at 85 unless they are closed. In other words, this only happens when the + signal from the SCM SP1096A arrives at the downstream side of the brake pressure switches on SP185L, using it to operate the relay by connecting it to 85. When the brake pressure switches are closed, the + signal from SP185L goes to ground though the relay. This would activate the relay, and the coil side of the relay would close the SP1081A circuit, passing + to the brake controller, therefore activating the trailer brakes. Since SP185L is always connected to chassis ground this won’t work. It is for this reason that I moved the relay activation connection to A, SP1096A. This is the point that goes high (12V) or low (ground) depending upon the status of the service brake pressure switches.

The way I interpret your schematic, 12v is supplied to SP1096A, potentially back feeding the SCM. When the brake pressure switches are closed, the circuit is closed to ground, and this activates the relay. This looks like the same effect as my design, but with the risk of back feeding the SCM? The connection to 85 (the coil -) is grounded through the brake switches to chassis ground at SPL-10. When the switches are opened then 85 floats to 12V provided by 12V on 86 and the pull up resistor internal to the SCM, shown as internal at B2. In other words the relay turns off. Floating up to 12V when the switches are open is a normal event in the OEM design, so it is not a threat to the SCM. I mentioned adding a flyback diode to the coil of the relay as an extra precaution to the SCM to avoid exceeding 12V that can occur due to the relay coil turning on and off. This is a typical precaution and a wise one.

What am I missing?
Hopefully, this is getting clearer. If not, I’ll add additional notes to your schematic that will help. We can talk by phone if you’d like. PM me and we can exchange info.

Post note:
After examining the schematic - again, I believe that the brake pressure switches are “normally closed” when the service brake is inactive (off). If that is the case, then use the normally closed contact 87A instead of the normally open contact 87. However, either way this still only deals with the trailer brake issue, and not the hazard light issue. Let’s get to a clear understanding of brake light operation and then we can circle back around to the hazards as they’re easy.

Once again thanks for all your work on this BonS.

Let me know if you think I am bogging the thread down and we can switch over to PM only.

It appears as though I have made some incorrect assumptions, and maybe have oversimplified the SCM and what it does.

So, here it goes:

I am on the same page that SP1018 supplies 12v for the trailer stop/brake lights, it does not power the brakes themselves. Power to the brakes is done by a 10 gauge wire and the 30 amp circuit SP709A. My wording in a previous post was poor.

My assumption for SP185L was that the completion of the circuit to ground and some type of “interpretation” by the SCM would result in the SCM energizing 1081A. I would interrupt the signal down 1081A with my relay. This could where my thinking jumped the rails. My logic was that the supply of 12v+ to 85 would also come from SP185L (only when the stop pressure brake switches were closed), as 85-86 would be hooked in parallel to ground with SP185L-SPL-19. Voltage would be shared by 85 and SP185L each to ground simultaneously, as 85 would be hooked in parallel to SP185L, with both terminating to ground (85 to 86 to ground via the relay and SP1085A to SPL-19). I am thinking I should have remembered one of the basics “electricity always follows the shortest path”. Why did I think 85 would always see any voltage at all when SP185L terminates to ground? Looks like I missed that one.

I have to admit this has become a brain twister for me. I have no experience with “control modules”. Hard to know what those suckers handle/process when the schematic only shows a dotted line representing a box with one resistor and a switch. You refer to normal events in the OEM design, and I have no knowledge in that area. I for sure want NO threats to the SCM. You obviously are a light year or two ahead of me on more than one of these fronts.

Your explanation makes sense. I will have to be sure to check the brake pressure switches to determine if they are normally open or normally closed.
I hesitate to ask this one… does the flyback diode get hooked up in parallel with the new wire to 85 preventing voltage from reaching the SCM when that the relay opens 85 - 86?

This will not be a quick mod for me, first finding the wires then very carefully inserting the relay and diode.

Let me know if I am on track.

Also, when the mod is in place and the engine brake is deployed without service brake application, the coach stop/brake lights will illuminate but the trailer stop/brake lights will not. That could result in a roadside conversation with someone...

Seems a shame that the activation of the stop/brake lights by the engine brake cannot be disabled as an option. Better yet a switch to give the operator the choice. As best I know there are truckers (especially owner operators) who have this “engine brake stop/brake light activation” disabled, as it apparently comes on some of the newer trucks. And… they have no brake issues with it as the truck/trailer brakes are activated by air pressure, but they still see it as undesirable. We as RV owners cannot have it done.

Thanks again BonS

[BonS]

I certainly don't mind working this out here as we're quite close to getting the circuit worked out. Tomorrow is a driving day for me and I get to test my engine brake mod on my CC.

It appears to be best to move the relay to the position shown by the red circle in the attached PDF. This interrupts the circuit before it goes to the coach brake lights. This will coordinate your coach brake lights with the trailer brake lights. In other words, your engine brake alone will not turn on your coach or trailer brake lights. Your service brake will turn on both.

The relay needs to be sized to handle whatever your coach brake light circuit is fused for but ignoring the current to the trailer since doesn't go through the relay. The flyback diode is placed in parallel with the coil of the relay. The cathode of the diode (the end with the stripe) goes to the coil + and the anode of the diode goes to coil -. A common 1N4001 diode is just fine. The nature of a relay coil is that it is an inductor. When voltage is interrupted (turned off) it produces a reverse-polarity high voltage in response. The flyback diode turns on and shunts this high voltage harmlessly.

Give me a day or two and I'll sketch a schematic that will give you everything you want plus a switch for mode selection. It'll be a single relay and two diodes.

Spartan Trailer brake with relay 2.pdf

[palehorse89]

Originally Posted by BonS

Good morning palehorse89. I'm not familiar with the Prodigy brake controller, but your description is clear. The PDF you attached shows a wiring scheme that serves the purpose of turning on the brake controller if you are just using the engine brake or the service brake, but it does not attempt to change the brake light logic in any way. Is that correct?

The Spartan schematic that we're referencing might/should apply to your coach. Have you given it a look and does it look like yours?

The approach we're discussing doesn't get involved with the engine Hi/Lo switch or PURPLE wire engine brake signal in any way so your Prodigy will work as normal if the modification discussed is accomplished.

PM sent

[BonS]

Doubling back to my post #1. I have the double-relay CC design in my '09 Allure. I can simply pull the relay marked "Engine Brake Load Relay" and the brake lights work exactly as desired. The engine brake doesn't turn on the coach lights or the toad brake lights so my Invisibrake in the toad doesn't activate the brakes due to the engine brake. I can tap the service brakes and all the brake lights turn on and my toad Invisibrake activates as expected.

On my next trip, this weekend, I'll reinstall the relay and cutt the "JUMP" jumper and repeat the test. I'll do this so that I can add a dash switch and select between OEM brake light operation and my preferred brake light operation.

[palehorse89]

Originally Posted by BonS

Doubling back to my post #1. I have the double-relay CC design in my '09 Allure. I can simply pull the relay marked "Engine Brake Load Relay" and the brake lights work exactly as desired. The engine brake doesn't turn on the coach lights or the toad brake lights so my Invisibrake in the toad doesn't activate the brakes due to the engine brake. I can tap the service brakes and all the brake lights turn on and my toad Invisibrake activates as expected.

On my next trip, this weekend, I'll reinstall the relay and cutt the "JUMP" jumper and repeat the test. I'll do this so that I can add a dash switch and select between OEM brake light operation and my preferred brake light operation.

Glad to read the relay being pulled and things work like you want. Sure do wish mine would be that simple!!!