I have looked on the forum but I cannot find the answer.

I have the electric deployable tow bar which is working fine, except for when we plug the lights in on one of our new trailers which has LED lights. It all works fine with the standard lights.

The problem is I can't use the automatic light test, I have to manually turn the rear parking sensors off and the trailer symbol on the dials doesn't illuminate when indicating.

I am aware this is because the lights are LED. Is there a little kit available to increase the resistance of the lights so that the car thinks that they are normal filament lights and all the towing assistance features work?

Thanks Range Rover SDV8

You add a resistor across each LED to LOWER the resistance not increase it, the value you work out from the wattage of a filament bulb. BMW i3 Electric Car
2012 Full Fat RR 4.4 TDV8 (now gone)
2006 VW Touareg 3.0 TDi V6

Hmmm - I also though it was to increase it

LED's have close to no resistance, so the current draw is so low it doesn't register. I though the resistor increased the load & therefore the current required - then the car could recognise it as a load & assume it's a bulb.

If resistance is low then current draw is high. LED's generally have a resistor in series to limit the current. The reduced current some cars cant detect / see it as a fail. By adding another lower value resistor across the LED (in parallel with it, not is series) the resistance of the circuit is lowered and the sensing system will be fooled into thinking a standard filament lamp is in circuit.

Standard ohms law

V
- = I
R

So if yo want a 21w load, the current needed in the circuit for the above wattage

W/V=I

21w / 14v = 1.5amps

Resistor calc

V/R=I

14 / 1.5 = 9.3 Ohms

Nearest value would be 10 Ohms. The relatively small current taken by the LED can usually be ignored for this.

Some LED lamps have the resistor built in to provide the load, oftem termed 'canbus compatible' etc BMW i3 Electric Car
2012 Full Fat RR 4.4 TDV8 (now gone)
2006 VW Touareg 3.0 TDi V6

Yup it is one of those scenarios where it is easy to think that when the common response is to add a resistor the conclusion is that it would increase resistance.

But as AJGalaxy highlights the resistor is to be added in parallel to increase the current and therefore resistance must be decreased. It is effectively adding an additional path through which it can flow. Same effect as opening another lane on a smart motorway, whilst it has still got restrictions, the additional flow means that the total flow increases....

These guys might be worth a call: https://sargentltd.co.uk/

They make and sell different kits for caravans with LED lights.

I think you’re right to get to the bottom of this. It is important that the computers in your FFRR know when it is towing. We had some tricky experiences in our L322 towing a new caravan until we had a Sargent box of tricks fitted to the caravan. 2004 L322 4.4 V8 Vogue Bonatti Grey
(205,500 miles and counting.......)

We had to fit a additional sergeant module for our caravan, so frustrating that this stuff is so difficult LED trailer lights are not new. Sold - Bell a 2015 MY16 Loire Blue Autobiography 4.4 SDV8
Previously George a 2007 MY07 Java Black VSE 3.6 TDV8
Previously a 04 MY04 Defender 90

Great, thanks for your help.

I will let you know how I get on. Range Rover SDV8