dad had a problem with his 91 d150. speedo worked odo did not. he had 4 other speedo's and they had a different back side than his orig 1. he tried to interchange them to get the odo to work but nothing happened. he finally called the speedo shop and got his orig 1 repaired. it was 160.00. bill's speedometer in bonne terre, missouri. only 3 wires on it. power ground and speed sensor, but i am sure you already know that.