Resistor for BRAKE lights Question

[Strat Tuner]

I put two 10W resistors inline with each brake light in the back. They keep CanBus happy.... but....
They appear to melting.

What is the fix for that???

Should I use a 30W resistor instead??

BMW r1200rt 2008

[Strat Tuner]

Inspecting the resistor, I see that the shrink on the outside is melted but not the white plastic underneath.
Obviously, that's not white plastic, or it would have melted too!
Still, the engineer in my heart tells me that the resistors need more ventilation, sooooo....

I've trailed them just outside the rear brake light enclosure in the rear tire well.

It doesn't make sense that something that HOT should rest against any surface down there as it's all plastic and not metal. It seems like it would have been best to surface mount the resistors on to a metal surface somewhere because the metal wouldn't melt, AND metal would help dissipate HEAT, which is my real enemy here.

The resistors are suspended by their own two wires (Red/Black) outside of any enclosure for maximum air flow. They stick out under the rear tire fender about an inch and a half (the length of each Resistor) ..... well away from the tire. Exposed to weather like that, they won't last forever, but what does?

The resistors ARE now surrounded by cool air, somtimes rushing cool air at speed, and should they burn up completely, they will fall off and into the street OR they will FAIL and break the circuit.

At either point, the CanBus will go sour and tell me something's wrong.

More specifics if you're not disgusted already.... I went for a three hour ride yesterday, and all that happened was that each resistor scorched a circular hole in the shrink protecting it. This suggests the heat is HIGH but also constant and NOT high enough to start a fire.

It's a little more "rube goldberg" (look it up) than I would like, but it's better than leaving the hot resistors tucked in with the brake light wiring in that confined, unvented, area just behind the actual brake lights.

Any thoughts? I would love to hear a better solution!
Different resistors? I don't know what will fix this....
or maybe this is just the way it is... for all resistors, and I have to accommodate it.

[Strat Tuner]

Here's a photo of the work. I added the red electrical tape strips so you could see where the resistors live now...

exposed_res2.jpg (209.18 KiB) Viewed 2296 times

[Doctor T]

If they are getting that hot to melt the outside covering, It sounds like they are getting too much current. Are they earthed correctly or somewhere along the line a wire is touching the frame?. They shouldn't need to be in an area where they are in the open air. I would check the wiring first before using a higher rated resistor.
Also are the new bulbs/LEDs drawing too much power?. This can burn out a resistor. The white bit in the middle used to be made of ceramic. These days heat proof plasitic may be used.
Personally I hate the Cambus system, old fuse box are a lot easier to work with.

[Stu]

I have resistors on an old bike when I fitted an LED rear indicators and mounted those to the frame to dissipate the heat

I never did feel them get hot or cause any melting of anything!

I am wondering if they are too small and you need larger ones so they aren't working as hard

From memory I am sure I used 50 watt resistors

[Strat Tuner]

If they are getting that hot to melt the outside covering, It sounds like they are getting too much current. Are they earthed correctly or somewhere along the line a wire is touching the frame?. They shouldn't need to be in an area where they are in the open air. I would check the wiring first before using a higher rated resistor.
Also are the new bulbs/LEDs drawing too much power?. This can burn out a resistor. The white bit in the middle used to be made of ceramic. These days heat proof plasitic may be used.
Personally I hate the Cambus system, old fuse box are a lot easier to work with.

(Please forgive my language if I use "earth" wire incorrectly. In the states, we say "ground" wire.)

• Too much current? It's a 12 volt system. How could they get any more/less than 12 volts? Lights use OEM hot wire connections.

• Earthed correctly? Earth wires connected to the earth wire that comes in the trunk under the seat.(common Brown wire)

When I first started this, I noted that the OEM earth connections for the two brake lights had failed. Took forever to figure that out!
I then back tracked to the earth wire in the trunk under the seat, tapped that, and ran my own black (earth) wires to the LED sockets.

I'm suspicious of that since it's my work.

Here's a question:
Would it be better to run a single, unbroken, earth wire from the black battery pole back to the brake lights to serve them? It would be "pure" in a sense as it wouldn't be interacting with ANY other earth wire.

[Strat Tuner]

I have resistors on an old bike when I fitted an LED rear indicators and mounted those to the frame to dissipate the heat

I never did feel them get hot or cause any melting of anything!

I am wondering if they are too small and you need larger ones so they aren't working as hard

From memory I am sure I used 50 watt resistors

I used 10W resistors because that's what you get when you search Amazon for "motorcycle turn signal resistor".

Amazon's TAG:

IHOTDER 4PCS Motorcycle Turn Signals LED Resistor,10W 12V Load Resistors LED Turn Signal,Universal Motorcycle Accessories Single Side Lead Decoder Resistor

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Resistor 10.jpg (178.92 KiB) Viewed 2217 times

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I do have the 50W metal ones as well, but those only have one RED wire passing through it. I should try those.

[Strat Tuner]

Examining the wiring diagram for the 10W resistor, I realize I have them wired in WRONGLY!
Consider this diagram, please:

Resistor 10a.jpg (236.11 KiB) Viewed 2215 times

There are SINGLE and DOUBLE wire connectors for both RED and BLACK (hot and ground (earth))

I have the "motorcycle" connected to both DOUBLE wire connectors, HOT and EARTH, and
the SINGLE wire connectors to the LED lights.

That is BACKWARD!
(that's what I get for reasoning it out on my own.) Maybe an electrician could tell me what effect that has on the resistors, but I suspect it's causing the over-heating!

The diagram says I should connect the DOUBLE wire connectors to the LED socket, AND
connect the SINGLE wire connections to "motorcycle".

That is the first change I will make.

Fortunately, the resistors are dangling out where I can reach them ... soooo....
I can
a) wire them correctly as per the diagram
b) wrap electrical tape around the resistor burn marks
c) go for a two-hour ride
d) check the tape after the ride to see if it burned through again with the CORRECT wiring. (I predict it will NOT.)

You got to love a wiring test that involves a two-hour test ride!

[David.]

Turn signal resistors obviously do not remain live permanently like the tail/brake light does.

I've viewed a video where the metal ones are used. If these cannot be mounted to metal bodywork, then in air is the next best thing.

If the Can-bus system is happy with the value of the resistors, just replace plastic with metal ones.

From what I can see of the turn signal resistors wiring, it's to connect them in parallel as they should be.

Higher wattage = more heat.

[Strat Tuner]

Turn signal resistors obviously do not remain live permanently like the tail/brake light does.

I've viewed a video where the metal ones are used. If these cannot be mounted to metal bodywork, then in air is the next best thing.

If the Can-bus system is happy with the value of the resistors, just replace plastic with metal ones.

From what I can see of the turn signal resistors wiring, it's to connect them in parallel as they should be.

Higher wattage = more heat.

I am grateful for your advice, thank you.

I've never had ANY electrical wiring classes, and that's probably why....

"In parallel" is not an expression that conveys any meaning to me.
When ever I see it, I just shrug and think "what does that mean? Can't the wires be Oblique? Perpendicular? Maybe even "at right angles"?? How about "rat's nest" which is what most wiring appears to be anyway ?!!"

In this case, I'll settle for "consistent with the wiring diagram" which does have meaning.

It's good to know that 50W would have produced MORE HEAT. Given that the wiring was done BACKWARDS, that could have been a bigger problem!

The failing, here, is mine. I'm sure Electrical Circuits 101 class would help.
:-)
(ssshhhhhh... after all this, I still don't know what "In Parallel" means....)

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[David.]

[Strat Tuner]

That diagram appears to be the first wiring scheme I improvised.
It doesn't match the wiring diagram the resistor maker gave.

Both behave the same. The resistors work but over heat!

Why did you post that, exactly?

It's my fault not yours. I am not an Oxford-class student.

[Strat Tuner]

Today's test did not go well. I had hoped that wiring the resistors closer to the instructions... as best I could.
The result?

burn1.jpg (191.23 KiB) Viewed 2080 times

It seems clear that using a 10W resistor would work for turn signals since the turn signal is ON well less than half the time.

Using the same resistor for a light that is ON constantly and gets even more ON from time to time, is a mis-use of the resistor.

There must be a resistor (or solution) for this, as I am NOT the first person to ever experience this behaviour.
Someone knows exactly how to fix this.
Someday, I hope to meet that person.

Until then... here is my solution:

a) I've left the resistors fully exposed to air flow underneath the rear tire enclosure. It is free there to too cool down as much as it can.

b) I've put a "quick connect" on the resistor's two black/red wires so that I can replace a failed resistor at the road side armed with only a fillip-head screwdriver. There's plenty of space to carry two spare resistors, pre-wired with the same quick connect.

c) As many, including Bill Murray, said "It Is What It Is".

Murray's comic translation is "You're FU**ED, and it's going to stay that way".
(It's in the movie "St. Vincent". It's a charming movie worth sitting for.)

I could certainly fix this by giving up and putting the incandescent bulbs back in the brake light sockets. I could then carry replacement incandescent bulbs. That would work... and depending how this goes over time, I may just do that.

[David.]

If the Can-bus system is happy with the value of the resistors, just replace plastic with metal ones.

The metal ones could be secured to the framework under the seat to dissipate the heat.

[Stu]

I really don't think they should be heating up that much!

If they are heating up a lot then they are working too hard!

I'm the same as you @Strat Tuner I too don't know enough to work it out

When I did the indicators on an old bike I was told to but the ones I got and wire them in like the diagram David provided and it worked with no issues
It worked so I never had to research any more