I bought the recommended wiring harness from etrailer for a 2009 JSW TDI and after looking at the installation instructions, took it to U-HAUL for the install. All the lights worked fine during testing. When I drove away, the glowplug light and subsequentially the check-engine light came on. The OBD-ii diagnostic code points to some sort of turbo filter do-hicky which (according to the mechanic) seems to be functioning properly. The JSW goes into "limp mode" moments after the glowplug light comes on (and starts flashing) How can the installation of trailer lights cause an engine malfunction?