LED brake lights cause Cruise Control to stop working


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WingAdmin
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LED brake lights cause Cruise Control to stop working

Postby WingAdmin » Sun May 04, 2014 9:36 pm



Once in a while I learn something new. Actually, I learn new things all the time, but this one took a bit of doing. :)

Over the winter, I replaced all of my rear lights with custom LEDs. I got everything together, and on my first ride out, discovered that my cruise control no longer worked. It would turn on, but ignored my pressing the "Set" button as if it wasn't even connected. The cruise control has always worked 100% before, so I had to assume something I did caused the problem.

I pulled the trunk off and took the cruise computer out. I hooked up a meter to the connector and tested all the signals from the various switches - brake, clutch, throttle disengage, and so on. Everything checked out 100% correct. I then had a look at the circuit:

Cruise Control circuit diagram
Cruise Control circuit diagram


The cruise computer monitors the brake lights - it has a connection right to the same wire that is turning the brake lights on. This is so it shuts off immediately when you hit the brakes. You hit the brakes, it sees +12V on that green/yellow wire, and shuts the cruise off. I started thinking - what if that wire needs to be pulled to ground in order to activate the cruise? Normally, it would be pulled to ground through the filaments of all the brake light bulbs. What if the various LEDs I had installed weren't presenting enough of a ground to allow the cruise control to activate? I decided to try an experiment. I added a SPDT relay to the circuit, so that when the brakes were not applied, the cruise control saw ground, and when the brakes were applied, the cruise control saw +12V:

Modified Cruise Control circuit diagram
Modified Cruise Control circuit diagram


I reassembled the bike and took it out for a test ride - and the verdict is, the cruise control now works again. So my hypothesis was correct: The cruise control not only disables itself when it sees +12V on the green/yellow brake line, it disables itself when it sees ANYTHING other than ground on that wire - and a floating input counts as "not ground".

So if anyone replaces their brake lights with LEDs and finds they can no longer set their cruise control, this is the solution.



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ka4yqi
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Re: LED brake lights cause Cruise Control to stop working

Postby ka4yqi » Sun May 04, 2014 10:43 pm

Thanks, yoU may have saved us a bunch of hair pulling. That somthing I can't afford to give up much of. I llike to change out my lights to leds in the future. Thanks again..

Steve

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Re: LED brake lights cause Cruise Control to stop working

Postby cbx4evr » Sun May 04, 2014 11:46 pm

What do you mean by "custom LED's"? I replaced my brake light bulbs with the eBay China LED bulbs you recommended some time ago. Haven't noticed any problems with the cruise.
"It´s a friggen motorcycle, it´s not supposed to be comfortable, quiet or safe. The wind noise is supposed to hurt your ears, the seat should be hard and riding it should make you s**t your pants every now and then. "

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Re: LED brake lights cause Cruise Control to stop working

Postby RBGERSON » Mon May 05, 2014 8:18 am

suggest this goes to a how to article..after a bit of time here.
HAD LOTS OF GOLDWING 75-83
NOW INTO 1500'S..RIDING A 1998 SE

FAIR WINDS,
RB

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Re: LED brake lights cause Cruise Control to stop working

Postby WingAdmin » Mon May 05, 2014 9:51 am

cbx4evr wrote:What do you mean by "custom LED's"? I replaced my brake light bulbs with the eBay China LED bulbs you recommended some time ago. Haven't noticed any problems with the cruise.


Custom LEDs as in I tore all of the lights apart and installed LED strips in all of them, instead of using LED replacement "bulbs."

LED strips installed inside lens
LED strips installed inside lens

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Re: LED brake lights cause Cruise Control to stop working

Postby thrasherg » Mon May 05, 2014 10:54 am

I would suggest, rather than going to the complexity of wiring in a relay, to just connect a resistor from the green/yellow wire to ground, use something like a 1K 0.5W resistor, that way there is negligible current flowing, but it will pull the wire to ground. Should be a lot easier and cheaper than a relay to install.

Gary

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Re: LED brake lights cause Cruise Control to stop working

Postby WingAdmin » Mon May 05, 2014 12:42 pm

thrasherg wrote:I would suggest, rather than going to the complexity of wiring in a relay, to just connect a resistor from the green/yellow wire to ground, use something like a 1K 0.5W resistor, that way there is negligible current flowing, but it will pull the wire to ground. Should be a lot easier and cheaper than a relay to install.

Gary


That was going to be my original fix. I originally tried putting a 470 ohm 1/2 watt resistor in there to pull it down, but it wasn't enough - it was still keeping it disabled. I knew 1157 brake light filaments are 21 watts, and that the OEM bike has two of them, so that's 42 watts, or 3.5 amps, which works out to around 3.4 ohms. I had a 100 watt, 4 ohm power resistor, and was going to stick that in there, but the brake sense wire on the cruise ECU was very small - looked like 28 gauge, and nowhere near enough to handle the 3 amps that resistor would draw. I could have stuck it elsewhere on the brake light circuit, but then I would have had to find a place on the frame to sink the fairly large amount of heat it would produce, without melting any ABS bodywork.

I figured I could easily switch the cruise ECU input line between ground and 12 volts, without having the hassle of dealing with heat dissipation (not to mention wasting 3 amps of perfectly good power as unwanted heat) by simply using a relay - so that's what I did.

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Re: LED brake lights cause Cruise Control to stop working

Postby thrasherg » Mon May 05, 2014 6:20 pm

So what is causing the green/yellow wire to float to 12 volts? If you need less than 500 ohms to pull the wire down, it's not really floating, something is supplying significant current to hold it high!! Given that a 480 ohm resistor was insufficient, then your relay looks like the best solution, but I would have expected a 1K resistor to be sufficient!! If I had the same bike I would be digging in a bit further to find what is supplying so much current that the 1K could not discharge the wire!! But your fix is just fine, but more work than I would have liked!! :lol:

Gary

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Re: LED brake lights cause Cruise Control to stop working

Postby WingAdmin » Mon May 05, 2014 10:50 pm

thrasherg wrote:So what is causing the green/yellow wire to float to 12 volts? If you need less than 500 ohms to pull the wire down, it's not really floating, something is supplying significant current to hold it high!! Given that a 480 ohm resistor was insufficient, then your relay looks like the best solution, but I would have expected a 1K resistor to be sufficient!! If I had the same bike I would be digging in a bit further to find what is supplying so much current that the 1K could not discharge the wire!! But your fix is just fine, but more work than I would have liked!! :lol:

Gary


It was 470 ohm, not 480 - typo (now fixed).

Also keep in mind that it's the 470 ohms plus whatever the resistor value is to run the LEDs off 12 volts (or current regulator, or whatever it is they do in there).

It only took me 15 minutes or so to rig up the relay, and I really just wanted to get it done and working, so I was happy that it was working. :)




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