BMW X5 Brake Controller and TM

Has anyone had experience, good or bad, relating to the availability and installation of a brake controller on a BMW X5 SUV? Most of the brake controllers commercially available have an asterisk next to them that say not recommended for BMW X5. My BMW dealer referred me to a local truck and hitch dealer and service center in Colorado Springs (Layton). Layton mentioned that they will not touch a BMW X5 with a 10 foot pole. I know it’s been done, but there is some difficulty interfacing the controller with German engineered internal vehicle braking systems.

[Bill]

I have no specific knowledge, but I seem to recall that the issue has to do with the brake light switch. In most cars, the battery is connected to the brake light switch, which is then connected to the lights. The other side of the lights go to ground. In this car, the brake light connection point is normally at 0 volts, and goes to 12 volts when you step on the brakes.

In some cars, the order is reversed. The battery is connected to the lights, the other side of the lights is connected to the brake light switch, the other side of which is grounded. In this car, the brake light connection point is normally at 12 volts, and goes to 0 volts when you step on the brake.

If you have an "unusual" car, and if this is the problem, there are a couple solutions.
1. I think I have seen a commercial device that un-reverses this situation. It is not complicated - just a simple relay - but if it is not commercially available, the dealers wouldn't know what to do about it.
2. Buy a brake controller that doesn't connect to the brake lights, and hence doesn't care what they are doing. There are not many of these. The Jordan Ultima (which I have) is one. I think there is also a hydraulic-to-electric converter that Rocky Mtn Ray used to drool over. You may find it by searching his posts.

Bill