soldered three resistors (3.3 Ohms each) inside a trailer adapter from Wal-Mart (Hopkins 7 Blade to 4 Flat Adapter with LED Test Lights: Automotive : Walmart.com), each resistor to ground from the left, right signals and the tail light.

As a result, when the adapter is connected to the car, the computer thinks that a trailer is hooked up and therefore the rear PDC and the manual ride height are disabled.

Beneficial when a bicycle rack or a cargo tray are connected...

I still need to test this adapter when a REAL trailer is hooked up, but in 7 years I had E53 (two cars), I towed a U-Haul only once... So, we'll see when I get that chance to test it...

I just keep the modified adapter in the trunk, so I don't lose it when I need it for the tray or the bike rack...