How to Install a Trailer Brake Controller in a 2003 Jeep Liberty and 2006 Mercedes ML500

Question:

I have a 2003 Jeep Liberty Sport 4x4 3.7L with a factory installed class III tow hitch with a 7 pin connector... is the Tekonsha 90195 P3 a good brake controller to use and is there a quick connect adapter available for this jeep? I also have a 2006 Mercedes Benz ML500 AWD 4x4 with a factory installed class III tow hitch with a 7 pin connector... is the Tekonsha 90195 P3 a good brake controller to use with this vehicle and is there a quick connect adapter available for this Benz?

asked by: Craig A

Expert Reply:

First, I will say that the Tekonsha P3, # 90195, is an excellent brake controller and would work well on both the 2003 Jeep Liberty and the 2006 Mercedes ML500. This brake controller is compatible with electric brake systems and electric over hydraulic brake systems. It also includes a multi-color display and can run diagnostics.

The only thing is that you will need to hardwire the controller in both vehicles because a quick plug-in adapter is not available for either vehicle. But installation is not very difficult. First, in order to easily switch the controller between the two vehicles, you will need an additional universal wiring harness, # 7894.

You will also need two 20-amp circuit breakers, # 9506P (for a trailer with up to 4 brakes) or two 30-amp circuit breakers, # 38630 (for a trailer with 6 to 8 brakes). And you will need some wiring, at least 40 feet (20 per vehicle) of wire # 10-1-1. A circuit tester like # PTW2993 may also be needed if you do not already have one.

Start by finding a good place near the battery to mount the circuit breaker on each vehicle. It will need to attach to a bare metal surface. Next, mount the controller in the vehicle according to the installation details I have provided.

To wire the controller, you will need to attach one end of the wire to the blue wire on the controller wiring harness. It will need to be route through the firewall and under the vehicle, avoiding areas that may pinch or burn the wire, all the way back to the 7-Way. At this point, find the wire for the electric brake output at the back of the plug (should be in the 7 o'clock position if looking at the back of the plug where the wires attach). Disconnect this wire and install the wire you ran in its spot. Save the excess wire.

Back in the cab of the vehicle, use the excess wire and attach some to the black wire on the brake controller wiring harness and attach another, separate length to the white wire. Route both wires through the vehicle firewall and into the engine compartment avoiding hot or moving parts. The wire from the white wire goes to the negative battery terminal. Save any excess wire. The other wire will go first to the circuit breaker. use any excess wire to then go from the circuit breaker to the positive battery terminal.

The last connection is the red wire on the brake controller wiring harness. You will use the circuit tester to test the wires on the brake switch located above the brake pedal. Find the wire that carries a signal ONLY when the brake pedal is pressed. If you find a wire that shows a signal when the head lights are turned on or the turn signals are engaged, it is not the correct wire. It needs to be a dedicated brake light wire and nothing else. You can use a quick splice, # SWC501746-1, to tap into the brake switch wire.

Follow the same instructions for both vehicles. You will then be able to move the controller from one vehicle to the other by simply unplugging it and removing it from the mount. I have included some links to an FAQ and a video that should help you. Since you already have 7-Ways on both vehicles, you can skip those parts.