Everything except for the Bosch relay can be purchased at Home Depot.
Here is a basic layout of what you will be wiring. Use is JUST FOR REFERENCE!:
DO NOT wire terminal #30 to the power supply as they showed. Use terminal #87 as I said in the previous post. This allows for normal operation due to any relay failure.
Follow my connections and you will be fine. For example, they use terminal #86 for the ground and #85 for (+). I use #86 as (+) and #85 for ground. This is the correct polarity for a Bosch relay. It will still work their way, but why not do it the correct way.
Most of your wiring will be in the engine bay. No need to tap into the light switch in the cabin.
Remember, a relay is just an electro-magntic switch. You are using a low current circuit to control an electrically independent high current circuit.
Since John will be helping with the connections, I'll let him help with the layout and where things will go. I don't know if he will suggest using 1 relay with the lights running in parallel or 2 relays with each controlling one light. If Bosch has a DPDT relay, this will make things cleaner and less wiring. I checked, but couldn't find a DPDT from Bosch.