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bosch



Member Since: 20 Jan 2012
Location: Kent
Posts: 18

United Kingdom 2018 Range Rover Autobiography SDV8 Corris Grey
Towing with LED trailer lights

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

Post #587020 11th Mar 2021 12:11pm
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AJGalaxy2012



Member Since: 11 Jun 2018
Location: Gainsborough
Posts: 1446

United Kingdom 2012 Range Rover Vogue SE 4.4 V8 Bonatti Grey

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

Post #587111 11th Mar 2021 8:33pm
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Alistair



Member Since: 11 Feb 2011
Location: Peterborough / Bordeaux / Andorra
Posts: 7724

United Kingdom 2013 Range Rover Vogue SE SDV8 Santorini Black

Hmmm - I also though it was to increase it Confused

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.

Post #587132 11th Mar 2021 9:43pm
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AJGalaxy2012



Member Since: 11 Jun 2018
Location: Gainsborough
Posts: 1446

United Kingdom 2012 Range Rover Vogue SE 4.4 V8 Bonatti Grey

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

Post #587143 12th Mar 2021 4:47am
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Bl4ckD0g



Member Since: 16 Feb 2020
Location: 127.0.0.1
Posts: 1322

Netherlands 2010 Range Rover Autobiography 5.0 SC V8 Santorini Black

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....

Post #587145 12th Mar 2021 5:50am
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TomV8



Member Since: 25 Sep 2017
Location: Yorkshire
Posts: 107

United Kingdom 2004 Range Rover Vogue 4.4 V8 Bonatti Grey

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.......)

Post #587150 12th Mar 2021 8:17am
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TJH1985



Member Since: 11 Feb 2015
Location: Nottingham
Posts: 663

United Kingdom 2007 Range Rover Vogue SE TDV8 Java Black

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 Sad

Post #587154 12th Mar 2021 9:11am
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bosch



Member Since: 20 Jan 2012
Location: Kent
Posts: 18

United Kingdom 2018 Range Rover Autobiography SDV8 Corris Grey

Great, thanks for your help.

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

Post #587444 14th Mar 2021 3:55pm
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