Mac 2

I just bought the truck with this issue it has code 4-1 speed sensor engine is derated low power I replace the speed sensor 1 turn back out after bottoming out as it says the old one was plastic had a lot of oil and grease on it so the ring is not loose I repaired the oil leak and went ahead to test drive and still speedometer not working and still no power I don't have a wiring diagram to trace the problem.