Thread: Discovery 3 LED trailer lights

Originally Posted by S3ute

Hi,

There are several previous posts on this.

You can get a special (and expensive) adaptor as others mention.

However, on the advice of my local auto electrician I fixed mine for about $4 using two small bulbs from Jaycar wired inside the trailer plug - hook one bulb onto each indicator terminal and unite the earths of both onto the common earth terminal. This creates sufficient draw to let the system know that the lights are there.

Had mine wired this way for over a year and it works fine.

Cheers,

I can understand that inserting the two small bulbs, (or I suppose two resistors), should create the conditions to allow the green trailer light to display and hence the 3 then knows that a trailer is connected. What I wondered is do the LED trailer lights do what I call the "twinkle" thing where they dimly light up ever few seconds? If so, it really of course does not matter even though it is not something I personally like seeing.

Originally Posted by bbyer

I can understand that inserting the two small bulbs, (or I suppose two resistors), should create the conditions to allow the green trailer light to display and hence the 3 then knows that a trailer is connected. What I wondered is do the LED trailer lights do what I call the "twinkle" thing where they dimly light up ever few seconds? If so, it really of course does not matter even though it is not something I personally like seeing.

I think people are confusing the two issues - the "twinkling" occurs only with the older D3's. It's not an issue with the D4 (as it has its own LED's!).

The resistors or globes in parallel with one of the indicator circuits will enable the sensing of a trailer with LEDs. Obviously for a D4 this is sufficient.

With the D3, one also needs to address the pulsing ("twinkling"), hence the need for relays.

Cheers,

Gordon

Originally Posted by gghaggis

I think people are confusing the two issues - the "twinkling" occurs only with the older D3's. It's not an issue with the D4 (as it has its own LED's!).

The resistors or globes in parallel with one of the indicator circuits will enable the sensing of a trailer with LEDs. Obviously for a D4 this is sufficient.

With the D3, one also needs to address the pulsing ("twinkling"), hence the need for relays.

Cheers,

Gordon

That is about the best clarification of the issue I have read. It also explains the different results people get implementing the various solutions.

Gordon. Where were you 70 posts ago. Well said, clears up a lot of questions.

Originally Posted by gghaggis

The resistors or globes in parallel with one of the indicator circuits will enable the sensing of a trailer with LEDs. Obviously for a D4 this is sufficient.

OK, this might be a stupid question...but here goes.

Why is it only necessary to add resistance to the indicator circuits? Doesn't that mean the D4 will sense the presence of the trailer only when the indicators are used?

Surely it needs to sense the presence of the trailer regardless of whether the indicators have been used - for example to switch of the reversing warning, turn on the advance tow stability assist etc?

The method that the D4 (and others) use is to send a pulse signal down the line to detect what is there (as well as non functioning lights). It this pulse that causes the LED's to mimic Christmas Tree lights. The resistor acts as a globe for the pulse signal and tells the ECU that everything is there and good.

Yes, I understand that, but things still don't seem right.

If the pulse is what is required to detect the trailer - why the need for the globe (ie for the additional resistance)?

If the globe (or other means of additional resistance) is the means of detecting the trailer - how does it work on the indicator circuit (which is where Gordon suggests installing the globe)?

It seems to me it must work under one of three scenarios:

a) there must be a pulse sent down the indicator circuit as well as the brake circuit - which means on a D3 the indicators must flash/twinkle as well as the brake lights; or

b) there is no pulse sent down the indicator circuit -instead the car waits for the indicators to be used and then senses the additional load and switches to trailer mode; or

c) the presence of a trailer is not detected by any signal on the indicator circuit and instead relies on the pulse sent down the brake circuit - in which case it seems Gordon's advice should be to install a globe on the brake circuit not the indicator circuit.

Obviously option b) is stupid - but what about a) and c)?

Ok,
2 vehicles with 2 outcomes but same fix.

D3 LED trailer connected, indicator lights flash as per Hazard button pressed. But not recognised.

D4 LED trailer connected, indicator lights do not flash. But still not recognised.
The D4 was designed to rectify the flashing issue but still the load pick up was not.

Therefore a "Load" must be placed in between tow vehicle & trailer.


Lets say for example(D3) Indicators.
Front 21w x 2 +
Side repeaters 10w x 2 +
Rear 21w x 2 =104w.
The target load would then be 104w + 21w x 2 or 146w (trailer load) for the unit to function correctly.
All recognised & working correctly.
These are not exact figures but gives you an idea of how the system works.

Because LED's are used the wattage is much lower (anything from .04w to 3w) & when you add the figures (104w + 3w x 2 = 110w) they do not come close to getting to the target figure, hence why a dummy load on the indicator circuit is required.

I hope this clears things up a little.

Cheers