Discovery 3 LED trailer lights

OK, I have had a brain wave. Correct me if I am wrong, but I assume that what the D4 is actually sensing is current draw from the trailer, not resistance? A LED light can be considered to have almost infinite resistance (& therefore very low current draw)?

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Originally Posted by Graeme

Option 1 will achieve nothing as the resistance of the resistor is far greater than that of the section of wire so the current will flow along the wire, not the resistor.

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That was my gut feeling also. I assumed that the LED had negligible resistance when I originally posted, so I can see your point now.

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Option 2 will achieve nothing because LED lights draw so little current.

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The LED has high resistance so draws negligible current, so the load resistor is not going to help. OK I can see that now...

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Option 3 - why not just fit the load resistor without going via relay contacts? When there's no blinker power there's no current flowing through the resistor anyway.

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If I just fitted the resistor straight to ground, then it would work whenever the indicators were used regardless of whether a trailer was connected, therefore invoking the D4 trailer modes etc. when there was no trailer connected.

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Originally Posted by Meken

If it's a D4 then a 21w load resistor wired in parallel (ie one end attached to indicator +ve and other to ground) should make it recognise a trailer attached. Beware those load resistors get extremely hot!) If you wire something into the car - the car will always think a trailer is connected thus turning off the rear parking sensors, changing the learning / changing traits of the transmission and who knows what else ? Why not cough up the cash and buy an led module that is the In car mount with the switch to turn on (trailer attached) or off when no trailer. Search led module - the the led module one. & pulsebusta - also come with a warranty :)

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A switching mechanism is required to avoid the vehicle thinking there is a trailer connected all of the time. The "off the shelf" modules use a manual switch, which I am trying to design around as I know I will either forget to switch it on off all of the time, which will annoy me.

I rekon its **** poor that we should be having to sort this out.Its a problem for LRA.MOST new trailers now are LED,the D4 should be able to cope with it.Will be discussing this with my dealer next week,especially since they told me my vehicle is LED friendly when asked at delivery:mad::mad::mad::mad::mad::mad::mad:
Andrew

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Originally Posted by cjc_td5

That was my gut feeling also but how come the wiring circuit on the Narva packaging is as follows?

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The Narva diagram has the resistor in parallel with the LED light, not in the power wire in series with the LED light - a big difference. The Narva circuit has the resistor between power and earth through which power will always travel.

I didn't intend to suggest that the resistor be permanently wired without the use of a switch, only that the relay was superfluous.


My 2010 D4 leaves the reversing sensors disabled if the trailer plug is disconnected until the ignition is turned off then on again. If there was a way to tell if the whole vehicle still thought the trailer was attached (eg gbox for gear shift patterns and ABS for trailer stability, if ABS actually uses a trailer attached indication in its trailer stability assist logic of which I'm unsure) then I could build a module that only sends the first blinker pulse through a load resistor to setup the trailer attached condition but thereafter exclude the load resistor from the circuit so that it doesn't get hot and also doesn't draw current so as to lessen the battery and alternator loads. Note that I have no desire to have the instrument indicator flashing by virtue of a dummy load resistor fitted in the D4 as its not doing its intended job of showing that the trailer light is working. However I don't know of a way to determine if the whole vehicle is remembering that the trailer was attached but it could be only the parking sensor module that is not clearing the condition, in which case a once-only module is not going to do the job. Perhaps Faultmate shows it in the gearbox status - I might have look when BBS fix their latest s/w to allow access to the TCU. Furthermore later model vehicles could use different logic in any/all ecus so something that works on mine can't be guaranteed to work on others.

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Originally Posted by cjc_td5

That was my gut feeling also but how come the wiring circuit on the Narva packaging is as follows?
http://www.aulro.com/afvb/attachment...1&d=1410090462

Surely using your analogy that would mean that the LED globe would take all of the current and the resistor none?



OK I think I understand that...



If I just fitted the resistor straight to ground, then it would work whenever the indicators were used regardless of whether a trailer was connected, therefore invoking the D4 trailer modes etc. when there was no trailer connected.



A switching mechanism is required to avoid the vehicle thinking there is a trailer connected all of the time. The "off the shelf" modules use a manual switch, which I am trying to design around as I know I will either forget to switch it on off all of the time, which will annoy me.

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Graemes statement and the nava diagram are correct. What you are over looking is that the LED light array("globe") does not present the same electrical characteristics as an ordinary cable. Cable = low resistance (very) and the LED Array= high resistance(therefore low current draw). what you need to do is put the resistor across the terminals of the array(per nava pic) to provide an additional (not alternate) low resistance path for current to flow through. Current will take both paths (hence parallel), small current through LEDs and and high current through the resistor. With the resistor allowing higher current flow the car now sees the trailer.

In your option 1, all the current still needs to go through the high resistance LEDs thus not changing the nature of the circuit and the fact that the resistor is placed in parallel with wire means that you are effectively joining the two ends of the resistor together so no current will flow through it - which was Graemes point.

With respect, if you don't understand these basics then do yourself a favour and get a pulse buster if you want something in car that you can switch on and off.

So what about the narva 12pin flat sockets that have an inbuilt reed switch on the flap - you could use the reed switch in lieu of a manual switch - open the flap to plug in the trailer and the reed switch closes the circuit with the resistor in it ?

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Originally Posted by LandyAndy

I rekon its **** poor that we should be having to sort this out.Its a problem for LRA.MOST new trailers now are LED,the D4 should be able to cope with it.Will be discussing this with my dealer next week,especially since they told me my vehicle is LED friendly when asked at delivery:mad::mad::mad::mad::mad::mad::mad:
Andrew

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Andy,it's not only an issue for Land Rovers, It's an issue for any vehicle that monitors these circuits. That's why companies like nava make those resistors.

I would say that some time in the future there will be a menu option to allow you to tell the car what sort of trailer is attached and... if we are really lucky, auto-sense it.

To those who may be confused by my post #211, after I posted it I realised that it was wrong and edited it. Whilst doing that Graeme & SBD4 replied in posts #213 & #214 to my original post.

I now realise that the LED lights can be considered to have high resistance and therefore low current draw (Ohm's law). Options 1 & 2 are obviously not going to work then, so I need to work out a switching method for Option 3. The most simple method is a manual switch, the engineer in me is still looking for a "better" way. :):)

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Originally Posted by SBD4

Andy,it's not only an issue for Land Rovers, It's an issue for any vehicle that monitors these circuits. That's why companies like nava make those resistors.

I would say that some time in the future there will be a menu option to allow you to tell the car what sort of trailer is attached and... if we are really lucky, auto-sense it.

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.............and it's about time the trailer manufacturers came to the party.

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Originally Posted by Meken

So what about the narva 12pin flat sockets that have an inbuilt reed switch on the flap - you could use the reed switch in lieu of a manual switch - open the flap to plug in the trailer and the reed switch closes the circuit with the resistor in it ?

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This is a good idea but to signal the presence of the trailer to the vehicle's electronics rather than by connecting dummy globes/resistors.

Im going the dealer direction first,want it in writing how I deal with the issue if they cant fix it.
After that,our new spannerman at work is also an auto sparkie.He has a few ideas how to get around it.After explaining how I believe the D4 system works it seems the switched vehicle based resistor is the way to go.
Andrew