S.M.E.C. (Computer) short circuited from the coolant and/or water.
The SMEC on my 1988 Dodge B150 3.9L V6 auto is on the firewall to the right of the wiper blade motor.

Replaced it with one off a V8, mine is a V6 and yet it still fired right up.
Mine has 2 connections, one long one (top), and one short one (bottom), ontop of each other. Some models of the V6 have only the one long connector on top, and no short stubby conenctor on the bottom.

I am so happy I got it fixed. Its running perfect.

I am going to tape up the exposed wires and put on the plastic wire protetor.

It feels good wrenching on my own vehicles and fixing the problem.