Connecting trailer wiring harness

[X5Newbee]

I just installed a draw-tite hitch yesterday. I also got their trailer light/brake module and wiring harness.

Where is the best place to tap into the factory wiring?

I read somewhere that their is a factory trailer wiring connector inside the spare tire well???

Otherwise, I plan to mount the module in the left rear, under the CD/NAV, drill a hole for the wiring harness to go out to the hitch, and tap into the wires by the left rear light, while running the power wire to the battery and the right turn signal wire to the right rear light.

Does anyone have the wiring schematic for the rear lights? I got the BMW repair/service manual DVD, but I can't find any schematics on it. I will probably buy the hard copy service manual in the future.

As background, I am new to BMW, but have worked on cars as a hobby for many years.

Thanks in advance for any help/advice.

[JCL]

The factory wiring connector is under the rear floor near the spare tire, but you won't be able to use it. It is a connection for a specific BMW module (which comes with the BMW wiring harness) that translates the multiplex signals into outputs for the trailer wiring. If you want to tap into the lights, you need to do it at the rear corner lights, or close to them.

Do you have a converter in case your trailer is different (combination brake/turn or separate)? Just follow the wires back from the bulbs. If you don't get any codes from the Lighting Control Module (LCM) for unbalanced loads then you are good to go.

Don't drill any holes, there is a large hole in the rear pan for the factory wires to go out through, and you will need a rubber grommet approximately 1" to fill it (from memory).