Need help. 04 F150 Lariat 4x4. Have no backup lights. Have changed DTC on tranny, no power to rear at all in reverse. Harness grounds, bulbs & fuses all okay. All pulled fuses were sanded & cleaned. Also have no power to trailer backup light in trailer harness. Checked dark green/yellow stripe wire under cab. No power in reverse. Only thing I can see that's left is the freaking embedded, un changeable relay in the fuse box. I see it is a common problem but it lacks a common answer. Soooooo who can point the way?

 

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