It's something having to do with the smart junction box, as I was told a couple years ago when I installed my LED's. I guess it doesn't completely cut off power like a switch does but instead leaves a trickle going to the plug, and with an LED that's enough to light it up slightly. I dunno.
2005 Mustang GT Premium
C&L Racer, 93R Tune, SR UDP's, JBA ceramic LT's & catted shorty H, Magnaflow resonators, Hooker Aerochambers, Hurst Billet/Plus, "P" springs Spohn reloc brackets/lowers, J&M AL panhard bar, DIY brace, smoked markers/tail lights