I've used a kitchen or large garbage trash bag, folded over, under each wheel to assist in caster/camber measuring. The tool that I have is an old bubble gauge, but quite accurate. It was also quite cheap, less than $50, IIRC.
Grey is probably the carb anti-stall wire. You can ignore that. The PRNDL wire is brown or blue/red. And yes, the BU and NSS wires are all in the same plug.