Installing a Trailer Brake Control in a Range Rover III/L322/LM

Introduction
For heavy trailers, as mentioned on the main RR III towing page, you need provision for controlling the trailer's brakes, which in the US are usually electric. Unfortunately, the new Range Rover III wiring kit (see RR III Trailer Wiring Harness Installation Page) still has NO PROVISION for this. The blue brake wire is connected to the (Ford branded) 7 pin plug, but the instructions say "not used". Ironically, Land Rover's corporate parent (Ford) leads the industry in trailer brake wiring, with some new models actually having a factory trailer brake controller buiilt in. I don't expect Land Rover to be that advanced, but it would be nice if they could at least catch up with Chevy and spend the extra $5 to run a couple of wires behind the dash for an aftermarket brake control. All the popular controllers can be ordered with a Ford, GM, Chrysler or Toyota plug -- wiring the RR with a Ford plug would make the most sense. Meanwhile, we have to wire up the new Range Rover manually for a trailer brake controller, and the description below covers my own installation.

Choice of Controller
There are two main types of trailer brake controller. The least expensive are timer-activated, with braking effort increasing the longer you have the brakes on. More expensive but much better are the proportional inertia-activated units which sense the vehicle's deceleration and apply the trailer brakes in proportion to it. Some of these are pendulum-operated and require calibration according to the angle at which they are mouted, but the more expensive ones have solid state inertial sensors and require no calibration. I have had experience towing heavy braked trailers with five different previous tow vehicles and brake controllers, and can confirm from bitter experience that it is not worth economising on this item. In my experience, the cheaper, more crude controllers are especially annoying at very low speed when coming to a stop, or in stop and go traffic -- in order to get sufficient braking effort at high speed they have to be set so they jerk you around a lot at low speed. Like most things in life, you get what you pay for. (we are only talking about a $60-80 difference here anyhow).

I settled on the Tekonsha Prodigy, one of the more expensive and widely used units at the time of writing, but any of the more expensive controllers should do a good job. I ordered mine with the generic wiring harness that includes a plug to connect to the back of the device.

Positioning and Mounting the Brake Control
The controller needs to be positioned where it can be reached while driving, both for adjustment and for emergency trailer brake application. I decided to mount mine just above the storage pocket in the lower left of the dash. The only problem with this is that the OBD-II/diagnostic connector is located in the top of this pocket, so I had to be careful to allow continued access to it. The resulting positioning is shown in the photo a the top of the page.

Wiring Connections Needed
All trailer brake controllers use 4-wire connections as follows:
+12 Volts (black)
Ground (white)
Brake switch input line (to tell the controller when you are aplying the brakes) (red)
Output line to the 7-pin trailer plug (blue)

Dash trim panels removed

Access Behind the Dash
Some wires need to go through the firewall, and another along the inside of the firewall to the right hand footwell. This requires getting access to the area behind the dash. For more details on this, see the dash trim removal page that will be coming soon.

Probably the only panel you really need to get behind is the underdash closing panel -- the flat horizontal one above the brake and accelerator. However, getting it out entails first removing the vertical center console closing panel (beside the accelerator on LHD vehicles). Simply remove the one screw visible in this panel and then pull it off downwards, outwards and rearwards to disengage its remaining securing clips. Then you only have about 3 screws to remove to take out the underdash closing panel.You can now see a convenient gap above the front of the transmission tunnel where you can easily pass the brake switch sense line through to the right hand footwell.

To run the necessary brake control output line back to the rear of the vehicle, you will also need to remove the carpet trim panel along the door sill, and the footrest and surrounding trim at the foot of the "A" pillar. This in turn makes it easy to remove the left lower dash finisher panel in which the little cubby pocket is mounted, giving better access behind the dash and making it easier to make provision for running the brake control plug wires out through the back of the pocket itself. However getting this last piece off requires first taking out the flat plastic fasia end panel, very easy to do by just temporarily yanking the rubber door surround seal out of the way and popping the panel out with a screwdriver.

All these panel removal operations will be depicted in more detail in the dash panel removal page.

Photo: Lower left dash area with trim panels removed for access as described above. Dangling wires and plug are for trailer brake control.

Power Supply and Ground Lines
The +12 volt supply wire should be connected as directly to the battery as possible, via a 20-amp self resetting circuit breaker. (If you connect it to some vehicle circuit controlled by one of the interior fuse boxes, there is a risk of losing the trailer braking function when that circuit malfunctions or blows a fuse). Accordingly, it is desirable to run the power supply and ground lines through the firewall to access the battery. Fortunately, on the RR III one of the major wiring harnesses goes through the firewall just above above and to the left of the brake pedal. The harness is enclosed in a rubber boot where it goes through the firewall -- so I was able to expand it slightly to accmodate the additional wires (see photos below).

Note that as shown in the photos above, I removed the black electrical tape that sealed the harness to the rubber boot. Under the tape there is a gooey black insulating substance around the harness wires; I also unnecessarily removed some of this in order to see if I could feed the brake controller wire through with the other wires. In the event, this looked nearly impossible, and might also damage the other wires. So I decided instead to feed them outside the hard plastic sheath around the harness wires, but inside the much more flexible rubber boot. This avids the possibility of damaging the other wires. From inside the car, I found it easy to "feel" where the hard sheath was and feed the wires through outside it. To get them through the last inch or so, I pried the rubber sheath up with a pair of pliers to create a gap to push the wires into through. Then I protected them with spiral wrap and fed them under the HEVAC intake vents across to the other side of the engine to the battery compartment see photos below).

The jump start terminal makes a very convenient connection point for the +12 wire. From this terminal, the wire should go through a 20 amp self-resetting circuit breaker (available at any auto parts store) before the connection to the brake control. I mounted the breaker near the battery and ran the supply wire to it from the jump start terminal through an existing hole in the front wall of the battery compartment (see photos above). Make sure you get a good ground for the white battery control wire; the instruction manual warns against using steel parts of the under-dash structure which might not be well grounded to the chassis. I grounded it to the chassis using a self-tapping screw in an existing small hole next to the battery (photo above).

Brake Switch Sense Line
On most vehicles this can simply be connected to the mechanical switch behind the brake pedal that activates the brake lights. However the Range Rover LM, like its relative the BMW X5, uses a solid state Hall-effect sensor for this function, and connecting anything to it is not recommended. (The BMW X5 site has some interesting discussion on this topic). The sensor's status is detected by the Light Check Module (LCM) which controls all the vehicle's lights, so the best thing to connect to is the LCM output that tells the trailer ECU that the brake lights are on. (Do not select one of the other outputs that controls the actual brake lights, because these can carry bulb test signals even when the brakes are not on). You can intercept this "brake status" wire either at the LCM itself, which is located behind the "A" pillar trim in the right hand footwell, or at the rear fusebox where it enters the trailer ECU. This Blue/Black wire comes from pin 10 on the LCM connector C0937, (which is the one at the top of the LCM), and runs via the wiring harness to the rear of the vehicle. My RAVE manual does not give pinouts for the trailer ECU, but you can find the same color wire there and connect to it.

I decided to connect my brake switch sense line to the LCM, which was a shorter run of wire and meant I would only have to run one wire (the controller output line, see below) all the way back to the rear of the vehcle. Once you have removed the panels under the dash (see dash trim panel removal page), it is a simple matter to run the wire across to the right hand side of the vehicle behind the glovebox, and connect it to the appropriate LCM output wire (see photos below).

The LCM is mounted against the lower "A" pillar in the RH footwell. I found it convenient to dismount it from the pillar and remove the connector to facilitate access to the wires, but you don't really need to do this. The right hand photo above with the right hand lower dash finisher still in place shows how you could perform this connection without even removing that item (which also requires removing the fascia end finisher). In either case, you can use the blue jumper connector supplied with the brake controller harness to make the actual connection.

Controller Output Line
Running the (blue) brake controller output line back to the rear of the vehicle to connect with the unused wire on the official trailer harness means somehow getting from the left front to the right rear of the vehicle's interior. After some thought I decided to run this wire behind the dash alongside the brake switch sense wire to get to the right hand side of the car, then run it straight back under the sill plates and "A", "B" and "D" pillar trim panels. I had already removed most of these once before to clean up a milk spill in the rear passenger compartment, so I knew it wasn't too tricky. (More details on removing and replacing these trim panels see the separate page on this topic, coming soon). The following photos and description depict the routing I used.

The lower "A" pillar trim panel and front right sill plate were already removed anyhow for the previous step (connecting the brake switch sense line to the LCM -- see above). The next step is to remove the right rear sill plate (it simply pops up under the influence of leverage from a screwdriver), allowing you to pull the lower "B" pillar trim off. This also just pops out when you pry it with a screwdriver. There is no need to remove it entirely -- just pull the lower half of it out from the pillar toward the vehicle interior) to allow enough access to run the blue wire behind it (see photo below left).

**NOTE: The shop manual warns that your should make the SRS system safe before removing this "B" pillar panel. To do this, remove the ignition key and disconnect the battery for at least 10 minutes. The first time I removed the bottom of the panel I neglected this step, but since I was not removing the top part where the airbag is, I didn't seem to set off any explosions. However, as always, follow my shortcuts at your own risk!!

This gets us back to the rear seat, and we only need to get the wire behind the lower "D" post finisher to reach the rear fusebox, which is already uncovered from installing the factory trailer harness (above). First, pull off the upper trim finisher by pulling it out from the top. (This is easier if you pull off the adjacent section of rubber door seal). With this panel removed you can access and remove the two Torx screws that hold the top of the lower panel in place. Then, simply lift the lower trim panel up to release the pegs at its lower edge, so the entire panel can be removed. You should now have a clear shot for the blue brake controller wire's connection to the unused blue wire dangling from the recently installed trailer harness.

Reassembly Tips
You can now reattach all the trim panels you have partially or completely removed. As the manual so often says, reassembly is the reverse of removal. However there are a few things to watch out for. In most cases you can visually line up the various pegs and clips that hold each trim panel on before you give it the final push. In the case of the aluminum sill plates (called carpet retainers in the shop manual), there are two kinds of fixings that need to be lined up. The white plastic pegs on the outer edge of the plate slide freely along the length of the aluminum extrusion from which it is made, so first put the outer edge of the panel in place and line up these pegs with the corresponding holes in the floor. Then when you carefully lower the inner edge of the panel towards the floor, you can see if the longitudinal blades line up with the clips in the floor. If not, the floor clips can be slid left and right by hand until they do. When everything liines up you can push down on the sill plate to press it home. For more details see the upcoming trim panel removal page.

Parts Sources
Factory Trailer Wiring Kit:
Atlantic British -- has low prices on two versions of the kit with and without the 4-pin adapter
The Rover Connection -- low prices on all genuine parts including the towing kit

Brake Controllers:
After shopping around, I got my Tekonsha Prodigy brake controller at Camping World, where the non-member price is $155 and the "Presidents Club" price is $139. Subsequently, I found it was available less expensively through Amazon.com! Relevant Amazon.com links and some other sources I found for other brands of controller are listed below.
Amazon.com Tekonsha Search Results -- Direct link to Tekonsha products on Amazon.com (Tekonsha Prodigy was $119 last time I looked)
Amazon.com Trailer Brake Controller Search Results -- A wide variety of controllers at low cost.
NorthernTool.com also have a variety of brake controllers and replacement parts for trailer brakes.
JCWhitney.com have several brake controllers and various other towing accessories.
Partsamerica.com have brake controls and other towing accessories
AutoAnything.com have several controllers including the Tekonsha Prodigy

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Page revised February 9, 2012


View from lower left footwell with cover panels removed, showing the vehicle wiring harness going through the firewall. The connector and wires for the trailer brake controller are also visible.	Close-up of harness passing through firewall, via a flexible rubber boot. Note trailer brake wires entering the rubber boot.


Red brake switch sense wire threaded through gap above transmission tunnel to reach the Light Check Module mounted on the RH footwell "A" pillar. Top photo is view from left footwell; lower photo is view from right footwell, both with trim panels removed.	Red brake switch sense wire connected to Black/Blue wire coming out of top connector of the Light Check Module (LCM) -- the black box in this picture, mounted to the lower right "A" pillar. Corner of glove box is at extreme top right of photo (LHD vehicle).	Illustration of access to LCM harness without removing the right lower dash finisher and fascia end finisher. You can just dig the Blue/Black wire out of this bundle and connect to it.


Photo taken from right front footwell looking forward. Blue brake control wire is routed across from top left behind lower dash closing panel, then down lower "A" pillar to the door sill.	Right front door sill plate removed to allow routing of wire under it towards rear of vehicle.


View from right rear passenger footwell showing routing of blue brake control wire from front door sill (top left of photo), behind the "B" pillar trim, under the lower black plastic footwell trim, and along rear door sill (lower right of photo).	Rear footwell and door sill showing routing of blue wire back along sill up the rear wheel arch. Note lower "D" post finisher on inner wheel arch is removed -- see next photos.


Above Left: removing upper D pillar trim finisher by pulling it out at the top. Above Center: This exposes the Torx screws holdin the top of the lower trim finisher. Undo, pull top out and lift finisher up to remove. Above Right: With lower "D: pillar trim removed, brake control output wire can be routed up the wheel arch and behind the loadspace trim (no need to remove it -- you can see behind it) to the rear fusebox. Right: Blue wire continues back to connection with "unused" blue wire on trailer wiring harness. I used a standard automotive wiring connector (see arrow).