Something else to be aware of on 2020+ RT's - Brake switch issues!

[Jetfixer]

Curiosity got the better of me and I decided to disassemble the switch. I found the failure and got some new insight into the design of the wiring system. Turns out the switch simply opens or closes the red wires on one side, and the black wires on the other. When the brake pedal is released both are open due to the loss of contact on one of the slider pads. My switch failed due to arcing on one of the black contact pads as can be seen in the photos. This leads me to believe that the new superseded part was probably modified to add a stronger internal spring to the sliders' contacts. These ones feel pretty weak to me. The wiring diagram does not show these wires as two reds and two blacks; it just shows how they connect to the system harness at the connector. Black is ground for the lights. The red simply sends a discrete closed signal to the ECM to say that you've pressed the brake pedal. Brake pressure must be picked off from the VSS Antiskid module. These contacts are simply open or closed as depicted in the wiring diagram; no pressure signal is possible at this switch.

 

[Knizar]

I like your "Curiosity" . Thanks for looking into what maybe a future problem for 2020 RT's. Think I could probably tackle that fix may it be necessary some day.

 

[BertRemington]

This has been a great dialog and learning experience

Jetfixer -- thanks for those pictures. Switch construction as I expected. The Black (brake light power) wiper damage explains your observations:

My switch failed in a bizarre way. If I pushed lightly on the brake pedal, the brake lights would flash one time extremely fast. Think like an old flash bulb. If I continued pressing harder, the brake lights would come on and stay on while held. If I pressed even harder, they would go off and stay off. Confirmed using a sensitive ohm meter after getting to the connector.

However I'm wrong about the low pressure function being based on pedal travel. The Red (brake lever position) wiper provides the pedal-pushed signal to the ECM which forwards that information to the VCM via CANbus. Whereupon:

My understanding of the system is that if the brake light switch is made, the system waits up to 15 seconds to see a rise in brake pressure.

And that is the "low pressure switch" -- the 2014 pedal travel became the 2020 15-second delay which increases reliability and reduces complexity by moving the function from 2014's mechanical device to 2020's software algorithm. My preference for the 2014's LPS microswitch is looking rather decrepit.

 

[FrogmanDave]

Since I ride a 20 RT, thought I should pay attention to this thread. I soon discovered this is way above my pay grade. So I'm begging the Spyder Gods not to mess up my brake switch.

Ditto !!!

Ditto x 2. It is crazy the knowledge you guys have! Especially about things electrical.

 

[Jetfixer]

Jetfixer -- thanks for those pictures. Switch construction as I expected. The Black (brake light power) wiper damage explains your observations:


However I'm wrong about the low pressure function being based on pedal travel. The Red (brake lever position) wiper provides the pedal-pushed signal to the ECM which forwards that information to the VCM via CANbus. Whereupon:

And that is the "low pressure switch" -- the 2014 pedal travel became the 2020 15-second delay which increases reliability and reduces complexity by moving the function from 2014's mechanical device to 2020's software algorithm. My preference for the 2014's LPS microswitch is looking rather decrepit.

I misquoted some specs above. The system is watching to see if the brake light switch is activated for more than 2.5 seconds without building more than 10 psi of hydraulic pressure in the brake system. If this is the case fault code P0504 would be set.

 

[BertRemington]

Switch needs some improvements to increase lifetime

Picture 6 burnt black contact is bugging me. That degradation shouldn't happen with wiping action contacts, especially double-break/double-make contacts powering a small number of LED brake lights.

Except...

If you examine the beginning of the contacts, they aren't even. That means the wiping action is NOT DB/DM but rather single-break/single-make which is much more stressful current-wise.

From Carling Technologies:

Contact Types

Wiping action contacts are "self-cleaning" contacts that wipe or slide against each other when opening or closing a circuit. This wiping action helps prohibit the build-up of any non-conductive deposits on the contacts themselves. Wiping contacts are typically used in AC applications, but are also suitable for low voltage DC applications.

Wiping action contacts can include some limitations on current, voltage, and lifecycle, and they require some form of lubricant, such as grease, to facilitate movement. With repeated arcing, the level of contaminants can increase and be captured by the lubricant around the contact area. This could eventually affect the operation of the switch.

Slow Break or Quick Break aka Slow-Make or Quick-Make

When contacts separate, arcing or sparking can occur between the two contacts. Arcing can burn up the contacts and reduce the useful life of the switch. The arc resulting from a DC voltage will be greater and will last longer then the arc from an AC voltage, because DC current has a constant value in relation to ground and zero. Because of constant electrical flow, DC switches should ideally be quick break. Quick break circuits typically require less than 5 milliseconds to make or break. Carling AC/DC toggles and pushbutton switches utilize a quick break design.

AC current has a value that is always rising or falling in relation to zero. Whenever AC current reaches zero (120 times per second) it cannot create a spark. Because of this, AC switches can be either slow or quick break. Slow break circuits typically require 8-12 milliseconds to make or break. Most Carling AC rated switches utilize a slow break design.

I believe the following deficiencies led to Jetfixer's switch failure:

1. Use of slow-make/slow-break contacts for DC currents. [Design selection]
2. Uneven fixed wiper start points forces initial load current onto single wiper. [Manufacturing process]
3. Insufficient sliding wiper pressure and fixed wiper width for initial load current. [Design selection]

The BRP switch can be used for this application but needs some improvements to increase its lifetime.

A suggestion for those adding brake light-related accessories: use the brake light power for signalling only, either via a diode- or resistor-protected relay or a semiconductor relay to switch your accessory power. Otherwise keep a spare switch on the shelf.

 

[Knizar]

Picture 6 burnt black contact is bugging me. That degradation shouldn't happen with wiping action contacts, especially double-break/double-make contacts powering a small number of LED brake lights.

Except...

If you examine the beginning of the contacts, they aren't even. That means the wiping action is NOT DB/DM but rather single-break/single-make which is much more stressful current-wise.

From Carling Technologies:



I believe the following deficiencies led to Jetfixer's switch failure:

1. Use of slow-make/slow-break contacts for DC currents. [Design selection]
2. Uneven fixed wiper start points forces initial load current onto single wiper. [Manufacturing process]
3. Insufficient sliding wiper pressure and fixed wiper width for initial load current. [Design selection]

The BRP switch can be used for this application but needs some improvements to increase its lifetime.

A suggestion for those adding brake light-related accessories: use the brake light power for signalling only, either via a diode- or resistor-protected relay or a semiconductor relay to switch your accessory power. Otherwise keep a spare switch on the shelf.

Bert , Are you saying that having the extra blinking module added to the rear brake lights is hard on this switch?

 

[BertRemington]

It depends. If the safety blinker is low current and it probably is because they tend to be small, then you're okay. But I've seen some folks with multiple big brake-actuated lights on license plates, saddlebags, etc. And most certainly don't directly drive trailer lights -- use an adapter module with independent power.

But if it's a big concern for you, I'm willing to trade for my 2014 design.

Knizar -- I owe you some firm numbers -- any lighting load over 15W should get the relay.

 

[Jetfixer]

Picture 6 burnt black contact is bugging me. That degradation shouldn't happen with wiping action contacts, especially double-break/double-make contacts powering a small number of LED brake lights.

Except...

If you examine the beginning of the contacts, they aren't even. That means the wiping action is NOT DB/DM but rather single-break/single-make which is much more stressful current-wise.

From Carling Technologies:



I believe the following deficiencies led to Jetfixer's switch failure:

1. Use of slow-make/slow-break contacts for DC currents. [Design selection]
2. Uneven fixed wiper start points forces initial load current onto single wiper. [Manufacturing process]
3. Insufficient sliding wiper pressure and fixed wiper width for initial load current. [Design selection]

The BRP switch can be used for this application but needs some improvements to increase its lifetime.

A suggestion for those adding brake light-related accessories: use the brake light power for signalling only, either via a diode- or resistor-protected relay or a semiconductor relay to switch your accessory power. Otherwise keep a spare switch on the shelf.

I do believe that insufficient wiper pressure was the cause of this, and I hope that those springs were upgraded in the superseded switch. The springs in the sliding wiper are very soft.

 

[Jetfixer]

In case anyone needs one, Brake Light Switch part # 710005480 has been superseded by Part # 710008326.

 

[Knizar]

In case anyone needs one, Brake Light Switch part # 710005480 has been superseded by Part # 710008326.

Thanks Very Much !

 

[safecracker]

Great write up. Really enjoyed reading this thread. Bruce

 

[RayBJ]

Thanks for the excellent info in this thread!
I just replaced the switch on my 2020 RT with the new version. I was getting intermittent VSS faults and Limp Mode. I determined the cause based on slowly pressing the brake pedal and watching the brake lights. As the switch pin was pulled, the lights 1st lit. But as more pressure was applied and pin moved out more, the lights went out, then flickered on/off, then went on solid at full extent.
As a precaution, I removed the in-line brake light flashers previously installed. I'm guessing the added current fried the switch.
Anyone want a good deal on the flashers? :gaah:

 

[Jetfixer]

Thanks for the excellent info in this thread!
I just replaced the switch on my 2020 RT with the new version. I was getting intermittent VSS faults and Limp Mode. I determined the cause based on slowly pressing the brake pedal and watching the brake lights. As the switch pin was pulled, the lights 1st lit. But as more pressure was applied and pin moved out more, the lights went out, then flickered on/off, then went on solid at full extent.
As a precaution, I removed the in-line brake light flashers previously installed. I'm guessing the added current fried the switch.
Anyone want a good deal on the flashers? :gaah:

It's not the flashers, it's the original switch. I also have the flashers and they work just fine with the new switch.

 

[NateNC]

Just replaced mine on 2021 June Build 9500 miles so right before the new switch version. Had zero issues went on long ride out of no where cruise control kicked off and wouldn't engage. Thought nothing of it really then parked the RT in the garage and noticed the tail lights were on. Remembered this thread reached under and worked the switch back and forth and lights went out. Did a quick test ride and problem returned, dealer had the switch in stock he was willing to do it under warranty but do to service timeframe being a week out he gave me the switch. Took about an hour to do, I didn't remove all the plastics you can reach behind the main one, only two zip ties behind that area.