bought my 87ranger at an auction. Six months after i bought the alternator shorted out! alternator, upper pigtail, the wire from the solenoid, and the started all fried. Replaced all with new along with coil and the ecm. Now it loses power and dies! after 30 mins or so its good to go. No regular timing with it like short driving or long doesnt matter.
only heads up is when the heater slows down. if i kill all electrical lights/heater/radio it still dies just not as quick. alternator has been tested and passes fine and battery is new.

well i know that when i first dug my ranger out of two weeks worth of snow when i first got it the plug wires were bad so it would run fine for like an hour or two and then it would turn over but not start like it had a flat cylnder so maybe its one of the wires not the alt.?