I'm using the switched power as the main power lead, and the permenent power as the 'memory' lead. These are wired with the factory Audi iso harness. I switched the pins in the empeg plug, as I know Audi's and VW's are wired kinda funny. I used a multimeter to check the levels during installation. I didn't see any significant voltage in the switched power when the car was off, but maybe this somehow increases after the car's been off a while? As for the negative spike, I don't really know how to check for this. I suppose I could tear down the dash again (ugh) and check it, but it sounds hard to diagnose