Just installed a mechanical oil pressure gauge in the cubby hole.
I'm now to the point of hooking up the wires for the gauge light.
I'm going to tap into the wires that go to the light in the "big"
cubby hole.Theres a solid orange wire and a black wire with
an orange stripe. Which one is positve or does it matter on
12 volt systems.

 

get a test light...pierce the wire with it, then turn the dimmer up and down...whichever wire shows the dimming on the test light is the one to use