searching for hei wisdom

Before starting, verify that your distributor has 2 wires from the pickup to a double-bullet connector. I am not familiar with 1981 D150 trucks. I know that some later 80's engines used a different Hall-effect pickup with 3 wires. It requires a 5 V supply and puts out a different type of signal, so won't work with the HEI module. If you have that, you will need an earlier electronic distributor.