Thread: D4 not detecting trailer wiring

Do they get hot with the indicators on?

If not, something is wrong - need to be wired in parallel, not series as mentioned.

Originally Posted by veebs

Do they get hot with the indicators on?

If not, something is wrong - need to be wired in parallel, not series as mentioned.

I re-wired in parallel and now the green trailer light in the dash flashes on in time with the blinkers... Uh?

- 21w load resistors on each
- there is an electric braking system installed for the caravan .. ( not sure if that is helping cause issue with detection )
- there is an ECB bullbar fitted with parking and indicator led lights.

It’s meant to only show the trailer symbol when the indicators are on. That’s normal and indicates it’s working. The light is never solidly lit.

Originally Posted by DiscoJeffster

It’s meant to only show the trailer symbol when the indicators are on. That’s normal and indicates it’s working. The light is never solidly lit.

ok thanks. It's wired in and getting hot.

It raises the question for me though... am i getting all the features the car is meant to deliver when towing - such as as anti sway, different gear ratios etc...? to be honest I'm new to the Discovery and caravans, so not sure exactly how it's meant to behave when in combination.

Originally Posted by JAYRO

ok thanks. It's wired in and getting hot.

It raises the question for me though... am i getting all the features the car is meant to deliver when towing - such as as anti sway, different gear ratios etc...? to be honest I'm new to the Discovery and caravans, so not sure exactly how it's meant to behave when in combination.

Anti sway is there always, with or without the trailer wiring connected. It’s a function of the stability control function. Different gearbox profiles are supposedly enabled when you have the trailer wired in as you do so yes, you will benefit from that as well.

In my experience, when the car correctly detects that it has a trailer connected (via the turn signals- the car sends a milli volt signal down both L and R indicator every few seconds confirming it has a trailer connected) throttle response is modified, anti-sway (stability control) is amplified and vehicle braking is modified (I believe more bias to the rear brakes) and the EAS is also adjusted, so that the car does not auto level when stopped.

Im not sure if shifting patterns in the transmission are modified, I’ve not noticed. I have found that putting the transmission in S mode gives better performance, this is because the line pressure in the gearbox is higher in S mode, so it will hold gears longer, especially when towing. However I’ve had no dramas towing in “D” on long hauls.

I note that you also have electric trialer brakes on your camper, you need to ensure this is correctly adjusted so that the trailer does not “push” or “drag” the car when braking. If set up correctly, both car and trailer brake together. Combined with the cars ABS and braking adaptations, a very safe towing set up. I have the Tekonsha P3 electric brake controlled in my D4 and this allows me to adjust the voltage applied to the brakes, thereby adjusting how much braking is done. I found this handy as the camper weight changes each time depending how much water, camping gear, food, etc is stowed.

Hope this helps,

cheers,

Eric