Cruise Control Fix for LED Tail Light Bulbs

[TrickVert]

I installed LED tail light bulbs awhile back, and like others here, have been living without my cruise control since. The circuit below fixes the problem using one 5-pin 12VDC relay and a resistor. (I'm not sure that the 10-Ohm resistor is needed, but I didn't want to send the cruise sensor straight to ground.) Note: The Red/Light-green wire is cut to insert the N/O relay contact.

I hope this helps someone out.

 

[ttocs]

The way you have it shown there, the 10 ohm resistor would serve no purpose. Being between the coil and the normally closed side of the switch means that it opens when the relay activates and then that part of the circuit opens, meaning the resistor is no longer connected. IF you mean you put the 10 ohm resistor in series with the coil and not connected to the NC portion of the switch, that also is not needed.

 

[cobrajeff96]

ttocs is right. One opens, the other closes. And in either case, the resistor is never part of a complete circuit.

 

[ttocs]

that is unless releasing the 10 ohm resistor to ground is what tells the cruise to turn off rather than the 12v from the pedal. I never went led tails so I never looked into this problem.

 

[cobrajeff96]

With brake pedal not pressed (open circuit on brake) the 10Ohm/1W (which is a big resistor), there is continuity from ground through the resistor to the lamps and to the solid state cruise circuit... but with a wire that's normally supposed to be hot. Granted, in this state, there is no current flow from the brake pedal switch so maybe it's moot. But I wonder what would happen with such an add-on with the parking lamps on? Or maybe that's a separate circuit altogether which I think it is.

If ground integrity is the question, maybe the LED flasher relay can help with that.

 

[TrickVert]

The problem is that by design, the cruise module requires the red/light-green wire to be grounded for the cruise to work, and it finds this ground through the brake light filaments. When LED bulbs are installed, this ground goes away, and the cruise "thinks" the brakes are activated.

The circuit diagram shows the status when the brake pedal is not pressed, and provides the R/LG a ground through the 10-Ohm resistor. When the brake pedal is pressed, the relay actuates and replaces the 10-Ohms-to-ground with 12VDC to activate the brake lights which also deactivates the cruise.

Where the resistor is located allows it to be in the "cruise ground signal" circuit, but not the relay ground path.

 

[TrickVert]

Jeff, you posted while I was typing. That wire is only hot when the brake pedal is pressed. Otherwise, it's at close-to-ground potential through the brake light bulbs.

The parking lamps use a different filament, and turn signals and hazzards don't involve that R/LG wire.

And yes, the 1W resistor is overkill, but it's the only thing I had that was low resistance.

 

[cobrajeff96]

Makes sense to me.

 

[ttocs]

gotcha. Cool thanks for sharing/teaching.

 

[Pallgor]

My fix was to put regular bulbs back in. I still have LED back ups and license plate lights

 

[TrickVert]

That's not a fix, that's giving up!

 

[Pallgor]

When I had my LED back lights I wasn’t impressed and I want my cruise control back and I’m not gonna be doing anything that could malfunction my electrical system I have LED headlights and everything is fine

 

[ttocs]

I got a set years ago now and tried them out by putting the led in one side and I thought the output on the halogen was better/more even so I returned them.

 

[TrickVert]

I got a set years ago now and tried them out by putting the led in one side and I thought the output on the halogen was better/more even so I returned them.

I was concerned about that, too, and did the same thing. These are very even, and the lights are now ruby red instead of having an orange-ish cast. (I did retain the standard reverse lights, though.) I'd like to install LED bulbs up front, but nothing I've found has the deep amber color I want. They're all too yellow.

 

[J_lope82]

I’m glad I read this post. I was just about to purchase the led bulbs.