To light my bed lights up in the past I would use the grey / purple wire found in the driver's side kick panel. However, I'm using a relay on my new truck because there are so many more lights than previously and I want to be cautious. Given the wires will travel up the passenger side of the vehicle I was wondering if there is a trigger wire on the passenger side that indicates when a door is open (to turn the inside lights on). Does anyone know?

 

Yes. When I installed my Amp Research power steps on my 2010, I tapped into four wires behind the kick panel on the passenger side. You can access the installation instructions (to see which wire) here:
http://www.amp-research.com/products...ies/powerstep/