You have to get the truck warmed up and then hook up your timing light to the #1 cylinder. Mark the indicator, on the belt drive, so you can see it easily once you start the truck. Then you must short the TE1 and E1 connection in the diagnostic box next to the fuse panel, in the engine behind the battery. Loosen the nut on the distributor and start the truck. Light the timing mark and adjust the distributor till you get 10 degrees BTDC. ( note some are different so check the emission control label on the inside of the engine compartment for your exact setting).
Remove and tighten connections and the shorting device.