A. I think the 87 2.6 is wired different re the temp switch. It turns o/d (and iirc, a/c) off when the motor is too hot. The temp sw. is normally closed, and is the ground for the o/d solenoid, IIRC.

B. I think you have the temp gauge wired to the temp switch noted above, NOT to the temp sender. The temp switch is the smallest sith single connector of the various temp thingies on the intake, on or near the tstat neck. The medium single connector thingy is the gauge sender, and is a thermistor, and the two connector thingy is the coolant temp sensor for the carb computer. The gauge pegs dead hot when the sender wire is grounded (you may have fried the gauge bimetal by now), and if it's hooked to the temp switch, it will be grounded unless you overheat the motor.

C. Charge the battery and try to start the truck in N. You may have a bad neutral start switch.