Installing the Tekonsha P3 Brake Controller in the 5 Series BMW E60 E61 Touring

Let's get the first question out of the way... Why? I've had my 2010 BMW 535xiT for almost 5 years now, and there is no sign that BMW will be importing the next generation 5 series wagon to North America - so I've decided to keep the BMW and run it into the ground. I purchased it at 78,000km, I'm at 175,000km now - averaging about 20,000km per year, so I figure I'll take it to at least 300,000km and really get my money's worth out of it. So - I already had the 1 1/2" receiver hitch installed and get routine service out of it with the bike rack, and I decided to properly set up the car for towing. There's going to be the guys out there that will say you should go out and get yourself an F150 or the like - and I've thought about this quite a bit. The 535xiT weighs 4100 pounds, has 300HP, and most importantly, 300 torques all the way from 1500 to 5000 rpm. Plenty for towing up to 3000lbs with the correct hitch. Oh - and the 535 touring is also equipped with airbag rear suspension, on board air compressor and self levelling suspension control.

The completed Tekonsha P3 Brake Controller Installation, Console Mounted, Passenger side of the Shifter

So - on we go.

Locating the controller - you want the controller within sight and reach of the driver, to be able to actuate the manual brake lever on the bottom of the unit for testing and calibration. One limitation of this controller is that it has to be aligned with the travelling direction of the vehicle (display perpendicular to the direction of travel) so that the inertial sensors work properly. The unit can be rotated up or down a full 360 degrees as long as the unit is aligned along the travelling axis. I originally thought I would install the unit under the drivers side dashboard (below the steering wheel) and there were a few nice options to do so - however - there is almost no clearance below the wheel between the drivers legs. You could easily avoid the unit installed under the steering wheel, but if you ever got in an accident, the placement of the control unit under the steering wheel could really mess up your knees - so - I looked for a better alternative.

I did a quick search on cell phone mounts for the E60 / E61 and found a nice placement to the right (passenger side) of the shifter - so I decided to fabricate a bracket out of aluminum sheet.

First step in bracket fabrication - hook over the leather border on the console, fit into the gap between the wood trim and the console edge. 

Final shape of the bracket, with a small hook to fit under the carpet trim on passenger side of the cabin. 

I glued a baseplate to the top of my bracket to take the screws from the Tekonsha mounting bracket, using isocyanate glue

You can see where the second Neodymium magnet will be fastened to the bracket - make sure you mark the rotation of the magnet with the correct field orientation - so when you mound the magnet on the back side of the bracket, it will engage with the hidden magnet with full force (N to S, S to N). 

 Now - onto wiring. The brake controller needs a battery connect, a ground connection, a brake signal from the brake light switch, and a switched line back to the back of the car, the brake connection on the trailer connector. I first tackled the brake light signal. This took a whole lot longer than what I expected, because the brake pedal switch on the BMW E60 / E61 is not connected directly to the brake lights. It's a double pole switch which switches to ground on one pole, and switches a signal between two control boxes - comfort access and lighting control module. So - I decided against tapping into the brake light switch wiring and tap into the brake light wiring instead.

There are four brake light bulbs on the 5 series BMW, and a single high mount brake light. Since the BMW has a light bulb failure detection feature, each individual light bulb has it's own feeder wire. That means that five separate brake light wires go from the lighting control module located up front to the left of the brake pedal, all the way to the back of the car. I decided to tap into the larger of the two brake light wires feeding the left rear brake light bulbs, this wire is 0.75mm diameter, gray wire with green stripe. I found this wire on the way out of the lighting control module.

Gray wire, green stripe, leaving connector to lighting control module. I've cut the wire and tapping the signal wire which will run to the Tekonsha P3 stop signal (red wire). 

By the way - there are two gray wires with green stripes in this section of harness, one is larger than the other, you need to tap into the thicker wire (0.75mm diameter). Don't ask me how I found this out.

Heat shrink butt crimp connectors - I use two layers of aluminum foil to protect the rest of the wires in the harness from overheating. 

 Now - I needed 20A feed, and a good ground. Just to the right of the center console, on the passenger side of the car, there is a conventional 12V power outlet up underneath the dashboard. Instead of tapping a new fuse on the fuse box behind the glove box, I simply crimped two space connectors on the Tekonsha harness and tapped into the connector for the 12V power outlet. Brown wire on the car harness is ground - connect to the white wire of the Tekonsha harness, and the other wire is the battery feed (12V) to the black wire on the Tekonsha harness. SIMPLE AND QUICK!!

12V power and ground - I just removed the connector from the passenger side 12V power outlet, and tapped into the connector using standard crimp on spade connectors. 

 Next - you have to run a minimum 14gauge wire back to the trailer connector. I ran this wire along the passenger side of the car. Pelican parts has some nice tutorials on how to remove the door sill trim - really useful - just google them - and I ran the wire along underneath all the door sill trim.

Use a coat hanger to help run the wires through B pillar trim without removing the trim piece

Tape the wire you're pulling to a section of coat hanger wire - to help feed the wire under the luggage compartment side wall trim.

Installation of the 7 pin connector underneath the car, to the right of the hitch receiver. I decided to trim the bracket to make the installation a bit easier. 

The completed 7 pin connector installation - bracketed to the underbody cover which hides the battery box and air suspension air compressor. 

 So - with all the wiring completed, back to the final bracket installation. I decided to have the aluminum bracket held in place using two neodymium magnets, one underneath the console side carpet trim, one underneath the Tekonsha mounting bracket.

I used my mythbusters / Adam Savage trick of mixing baking soda with Isocyanate glue to thicken the glue, and provide gusseting for the magnet. This is the backside of the thin carpet trim piece which runs along the passenger side footwell. 

Conclusion

With the brake controller installed and powered up, here's what it looks like in the 5 series. 

Powered up and tested, brake controller head unit conveniently located to the right of the shifter.

The Tekonsha P3 has a nice voltage troubleshooting screen under the help menu - will tell you your battery voltage, and stop light voltage. 

I also installed a Curt lighting adapter to provide the turn signals to the trailer adapter, I'll write a separate post on that installation, and one on the operation of the brake controller.

Sources and Links

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