Do you tend to idle this car a lot? I'm sure the harness is poorly made but idling any car for an extended period of time is a really bad idea for a number of reasons. The heat build up alone under the hood is enough to trash the wiring. In fact, car manufacturers don't even recommend "warming up" a car on a cold winter morning beyond a minute or two. Turn it off, it's better for the smog problem in Houston.
2004 E320 Wagon
1998 Range Rover 4.0 SE