Thread: LED trailer light shunting - a different thought??

Hi all
Thinking out loud here... I have built a caravan and yesterday finished the exterior lights which brings me to the famous LED issues.
To break it down there is 2 parts to this.

* A load is required to satisfy the testing, this stops the errors displayed on the dash and the fast flashing indicators. Solved with a resistor. The car now knows about the trailer and turns the rear parking sensors off & disables suspension height changes.

* The test pulse is 2v and causes the LED to flash continually. A relay inline to turn the lights on/off solves this. The relay requires ~6v to activate and allow power to the light.

I'm thinking I have 3 options and am interested in people's thoughts:

1 A shunt box plugged inline like the commercially available devices.
Essentially the car is now testing the box & the connection between the car and box. The car knows about the trailer.

2 A shunt box built in located down the back.
Similar result to #1, however the testing functionality is now testing the trailer plug and wiring to the back of the van. The box is soldered in place. I built a Camper trailer in 2008 and installed a box on the draw bar. The one occasion that the car reported errors it was a problem with the plug on the trailer - so it provided a limited test.

3 Something different - A two part approach involving relays and disabling the reporting.
I have a switch installed that enables off road height to be used while towing, switching this also removes the errors to the dash (as the car no longer knows about the trailer) and I've used it several times while towing a hire trailer to allow the indicators to flash normally. It does not stop the continual flickering so a set of relays would also need to be installed. Down side is there is no testing functionality at all - just like a Toyota.

I'm leaning to option 2, I removed the circuit board from the camper trailer when it was sold, so it could just be reused in a new enclosure. It is worth noting that the caravan has air suspension which like the car has 3 height settings and that switch will be used a bit... One thing I can't confirm is whether the car activates anything else when it detects a trailer (apart from parking sensors and height change lock out)

Over to the group for opinions, options or slander...

Ps - on the note of hire trailers - I hired a 3.5t plant trailer not long ago and quickly figured out a shunt box (or just the relays) was needed. It has a trailer mounted brake controller feeding the brakes in parallel with the incab controller (so it can be towed by a car without a controller). The 2v test pulse on the brake light is enough to lightly activate the brakes continually. I actually disconnect their controller and connected it back up before returning it.

Originally Posted by DaveKelly

Hi
I made up a little black box that I can plug in between vehicle and trailer. This allows me to change configurations depending on what lights are fitted to the trailer I am hooked up to.
I'll dig out the info and links next week - after Melbourne Airshow trip.
Cheers

OK - got my dates confused .... fly tomorrow.
This is an old topic and I found lots of comments on the net. But I settled on this one.
I made up a black box using Lawrie's circuit a year ago.
Lots of debate and discussion here: DISCO3.CO.UK - View topic - D3 not compatable to LED trailer lights
And photo/circuit is here: DISCO3.CO.UK Photo Gallery - Home > Member Galleries > lawrie50
Box currently works for me.
Pick up Aussie built Rangefinder caravan this month so will be interested to see if it works on it as well.
Note there is a reference to installing diodes across the relay coil in the discussions.
I think I have used IN4007's. Cheap as chips!
You can get significant voltages generated in the relay coil as the field collapses.
You don't want them getting out of the relay and back up the controlling circuits.
Hope this helps.
DK