Ford ignition modules are sensitive to heat. One of the guys I worked with used to drive a brand new truck off the assembly line every day as part of Quality evaluation. During the summer he would stop at a fast food place half way home and get a cup of ice to cool it down just to get home. Ford used to have an air condition relay and circuit breaker on full sized cars up under the glovebox. In the summer when the inside of the car would heat up. the ac would run for 2 or 3 minutes before it would kick the hot breaker.