what year is your truck? I see you mentioned obd1 to obd2 adapter. these ususally don't work. on a pre 96 (95 and older) there is no power wire in the ecm connector. you will have to supply power externally to the scanner if it doesn't have a built in battery to operate it. if your scanner is made for obd2 only and does not support obd1 systems, it wont work period. obd1 scanners are getting very hard to find nowadays unless you want to spend big money on something that supports them like to snap-on scanners. though on a 6.5 diesel enging, the snap-on scanners are not recommended and are known to give inaccurate readings especially when looking at the timing.
