D4 Electric Trailer Brake Wiring

Hi All,


Thanks for these excellent instructions.


Two questions:
1) I want to install a Redarc TowPro and am thinking of installing the control module in the Rear Left Compartment. This mainly so most of the wiring is kept there and it is not cluttering the underdash area. I can run 5m of RJ45 control wire to the dash control knob. Any thoughts on this approach?


2) I get why we need the Diode on the Brake Light input. What I don't understand is how the car and caravan brake lights are then activated when the brake controller is used. The brake controller light output would be blocked by the diode. I am basing this on the wiring diagram (heading is 17091 - Exterior Lighting) which shows the diode between the EBC and the trailer pickup.


Thanks for any thoughts.
Peter

Peter,

As I understand it, the trailer/van lights are activated by the car as per normal via pin 6 (red). The brake controller is not activating the trailer/van lights, just its brakes via pin 5 (brown). The brake light connection to the brake controller is only an input.

I seem to recall someone else having the module fitted LHR compartment, so long as the RJ45 is not too long as you say.

Cheers,
Scott

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Originally Posted by RoverLander

1) I want to install a Redarc TowPro and am thinking of installing the control module in the Rear Left Compartment. This mainly so most of the wiring is kept there and it is not cluttering the underdash area. I can run 5m of RJ45 control wire to the dash control knob. Any thoughts on this approach?

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I did essentially this with my Vogue. No issues at all.

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Originally Posted by BigJon

I did essentially this with my Vogue. No issues at all.

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Jon did you mount the module in the rear driver side or passenger side of the RRV?

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Originally Posted by RoverLander

Hi All,


Thanks for these excellent instructions.


Two questions:
1) I want to install a Redarc TowPro and am thinking of installing the control module in the Rear Left Compartment. This mainly so most of the wiring is kept there and it is not cluttering the underdash area. I can run 5m of RJ45 control wire to the dash control knob. Any thoughts on this approach?


2) I get why we need the Diode on the Brake Light input. What I don't understand is how the car and caravan brake lights are then activated when the brake controller is used. The brake controller light output would be blocked by the diode. I am basing this on the wiring diagram (heading is 17091 - Exterior Lighting) which shows the diode between the EBC and the trailer pickup.


Thanks for any thoughts.
Peter

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1. I just installed a Redarc tow-pro(in my D3) You'll see in the instruction that you can run up to 5m of RJ45, but I recon you'll struggle to be able to feed the cable connector from the rear to the front, as the cable needs to squeeze through some quite constricted spaces, so you'll probably need to attach the RJ45 connector to the cable after threading the cable.

I don't know why you'd want the unit at the rear though. I'd be mounting the unit under the console and powering it via the the black and white wires direct from the battery/earth through the firewall, with the circuit breaker mounted in the engine bay. Then you just run the red and blue wires to the rear.

2. The red wire is normally an input signal to the EBC. And the diode protects the modules. When driving normally you brake with your foot, the lights on the car and trailer are illuminated as you'd expect. That brake light current flows through the diode to the ECB and then the ECB applies the trailer brakes.

However, depending on where you've placed the diode in the circuit, when you press the RedArc's manual override button. It applies the trailer brakes as you'd expect, but it also sends a reverse current from the ECB to the car brake lights and illuminates them too. The diode, though must stop this current flowing in the reverse direction from flowing to the car's controller module.

You'll notice in the tow-pro instructions 2.4 Testing your Install it says that you test it by pressing the manual overide button. There are two things you should see. A. The vehicle brake lights should illuminate, But they will only illuminate for you if your diode is located correctly in the circuit. B. It also says that the trailer brake light output should illuminate the test lamp. That is wrong. They've made a mistake with the manual. It should say to connect the test lamp to the trailer brake output. (Ie. Wire the test lamp to pin 5 and not pin 6 as the instruction imply). Turn the dial up a bit when you do this because a setting of zero will send zero current through the test lamp, and nothing will show.

The earlier description by Sniegy for diode location was updated in this short post. . That's where you want the diode.

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Originally Posted by BSM

You'll notice in the tow-pro instructions 2.4 Testing your Install it says that you test it by pressing the manual overide button. There are two things you should see. A. The vehicle brake lights should illuminate, But they will only illuminate for you if your diode is located correctly in the circuit. B. It also says that the trailer brake light output should illuminate the test lamp. That is wrong. They've made a mistake with the manual. It should say to connect the test lamp to the trailer brake output. (Ie. Wire the test lamp to pin 5 and not pin 6 as the instruction imply). Turn the dial up a bit when you do this because a setting of zero will send zero current through the test lamp, and nothing will show.

The earlier description by Sniegy for diode location was updated in this short post. . That's where you want the diode.

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Am I reading it correctly that by pushing the towpro dash knob the brake lights on the car should illuminate, even with no trailer attached?

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Originally Posted by ScottD4

Am I reading it correctly that by pushing the towpro dash knob the brake lights on the car should illuminate, even with no trailer attached?

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Yes. Mine does.

I am a bit confused. I can understand the ECB reverse current applying the trailer lights because it is the trailer plug wire that is spliced in to with the red wire. But how is the vehicle brake light applied as well? I was going off the wiring diagram that someone posted to this thread a while back and I didn't appreciate there would be a connection to the vehicle brake light. Does the red wire we splice in to go to both the trailer plug and vehicle brake light?

I have put my diode in the wrong place (I missed the updated location in the other thread), so I want to get it right the 2nd time.

Cheers,
Scott

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Originally Posted by BSM

Yes. Mine does.

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Originally Posted by ScottD4

Am I reading it correctly that by pushing the towpro dash knob the brake lights on the car should illuminate, even with no trailer attached?

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Originally Posted by BSM

However, depending on where you've placed the diode in the circuit, when you press the RedArc's manual override button. It applies the trailer brakes as you'd expect, but it also sends a reverse current from the ECB to the car brake lights and illuminates them too. The diode, though must stop this current flowing in the reverse direction from flowing to the car's controller module. The earlier description by Sniegy for diode location was updated in this short post. . That's where you want the diode.

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Originally Posted by BSM

Yes. Mine does.

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Hmmm. Interesting. My wife and I just ran some tests. Mine does:

* Not illuminate the brake lights when pushing the knob (despite the knob glowing blue as per the book)
* Does not properly illuminate a test lamp when pushing the knob. If anything, the test lamp is flashing dimly continuously until the knob is pushed, then nothing happens.

We haven't towed a trailer with this yet, so I can't confirm it's operation with one attached. But I dare say something is a-miss.

Chaps, I have just realised that the D4 is a very different wiring setup than the D3. My fitting was in a D3. I just reviewed Sneigys instructions at the start of this thread and he says you don't need a diode for his D4 wiring setup. Clearly it's a different wiring arangement recommended here than for the d3. Sorry for giving you confusing advice.

All I can say is that where I have the tow pro connection in my D3 it does work as I have described.