I've got a question on grounds as a follow up on my relay questions. Please bear with me if this is meandering. Basically, I'm replacing my car HVAC controls with a PIC driven replacment. I need to work a few servos to control the cables, the rest is pretty much replacing the equivalent of mechanical switches. So I'm going through the schematics for my car and designing the replacment. Here's my question. Currently, the parts I'm replacing are grounded to one of two points, either in the engine bay (#13) or in the cabin (#5) Most of the switches are hooked up to the compressor controller and the blower motor and grounded through (#13), but there are a few switches that aren't (they go to #5) , those are the AC On/Off, Foot/Def and Inside/Outside switch. Seeming I'm using a ULN2803 for the fan switch positions, I'd like to use the one ULN2803 for all the switches for simplicity, but they share a common ground. I'm wondering if I'm opening up myself for problems here. Can anyone think of any reasons why the grounds might need to be seperate? I'm thinking it's probably just for the convienence of how the parts are assembled but I dunno.