Thread: Discovery 3 LED trailer lights

Yeah I'm with you Basil. But if it is that simple, I am still stumped as to why the U-haul adapter I purchased isn't sufficient. It obviously works for other brands of rigs with similar schemes. But thus far, the 100 ohm resistors built into the adapter and attached to both left/right and running lights lines, have not caused the vehicle to recognize the trailer. Or at least, the "trailer" light on the dashboard has never ever lit up.

I think I have found your problem.

The adapter you currently have, has a 100 ohm resistor in it. The D3 / D4 only require a 6 ohm, 21 watt resistor, wired in parallel.

Try this, and see how it goes. Should be able to get one for less than <$20.

Thanx Basil. I ordered some of the 6 ohm resistors today. Hope to have them by Monday. Man I hate it that the existing setup didn't work...since it was so nice and neatly packaged.

Thanx.

People are talking about D3s and D4s within the same thread without making a distinction between the two. My understanding is they are different and require slightly different approaches to fixing the trailer LED problems.

Both D3 and D4 attempt to detect the attachment of a trailer by sending a pulse down the trailer indicator wiring. When it detects the required resistance it assumes a trailer is connected and reconfigures the vehicle as required. Applying the appropriate resistance in parallel with one or both LED indicator lights on the trailer with cause both the D3 and the D4 to detect the trailer.

However, the difference between the D3 and D4 is the D4 only ever sends one detection pulse down the line, when the drivers door is closed. The D3, on the other hand, is continuously pulsing the line.

This pulse, whether on the D4 or the D3, will cause both indicator lights to flash simultaneously. On the D4 it does not matter because it only happens once just before you drive away. On a D3 it is a problem because it never stops while driving.

So the solution to LED lights problem on a D4 requires only appropriate resistors. The solution to the LED problem on a D3 requires appropriate resistors but also some means of filtering the trailer detection pulses from the system after the trailer has been detected. The pulse filtering is usually implemented by a using relays. That is why some trailer adaptor 'black boxes' have relays in them. They are required for the D3 but serve no purpose for the D4 and are not needed.

Like I say, that is my understanding. Hope I've got right.

With respect to the D3 Ferret, that is how I understand it. Two issues:

1) Trailer recognition as indicated by the trailer dashboard light illumination with the use of the turning signals: so as to disable the Parking Assistant and to allow the BECM to adjust power curves, shift points etc.

2) Eliminate the pulse light issue.


It appears that I do not have adequate resistors in place to resolve #1 (thanx again Basil)...but will in a few days. This issue is my primary concern...recognition of the trailer and the rig undergoing the adjustments to improve performance, economy (did I really just type this with a LR3?) and safety.

As for #2, pulsing LED's, this problem is resolved thru use of the relays. This I have already witnessed.

Thanx to all that have contributed...over the years!

If the D3 does continue to pulse the turning circuits then the relays is a simple way of filtering. The relays by themselves could be enough to look like an incandescent bulb. It will come down to how sensitive the detection circuit is!


Forgot to say, the reason the relays filter the pulses is that there is not enough energy in a sensing pulse to pull the relay shut whereas the turning signal pulse is much longer and does have the energy to pull the relay closed.

Relays with built in resistor may be adequate.

Although the pulses on my D3 are not enough energy to cause the 40 amp / 14VDC relays that I am using to close, the 79+ ohms of resistance the relay is providing, is not being recognized by the vehicle as a trailer being connected.