Without looking myself....I would suggest you try the main harness that runs along the door sill. I just looked at a DEI tech sheet and it said green/wht in the rearview mirror. I am not sure why it would be there, but they are usually very accurate.
I don't know of a source in the cab but, I do know that the backup light relay is located in the box just behind the battery. The lid snaps off and inside are all the relays. I used that as a source to energize another relay which switches power to some 55W aux backup lights.
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