What can make a PCM on 1994 F150 burn out? Both times the burnout happened after a heavy rain, but I live in Florida: There is always a heavy rain. It's like saying it burned out after a sunny day.

I have a 1994 F150 extended cab, 4.9L automatic with e-overdrive.
I bought it 6 months ago to pull my boat. In quick succession I had to replace the radiator and all hoses and belts, ignitions switch [I did that myself] battery, starter, PCM and windshield [it leaked, badly]. It still has a bad front fuel pump assembly [it directs gas to the wrong tank when I use the rear] but I'm living with that. It's been towed five times.

Doing anything once was ok, but the PCM burned out in five months. I trust the mechanic who replaced it [he worked on my 1990 F150 I bought new, and I didn't spend this much over 19 years]. Jowers replaced the second PCM for free [$800 for the first] but has no idea why it burned out. He found no water damage and could see no leaks when he tested it. There are no water leaks I can see now - but maybe the leak in the windshield causes the first PCM to go: that was why I replaced the windshield. There is no evidence of rust.

Now I don't trust the truck.

I know these trucks are generally reliable - my 1990 with a 5-speed stick pulled my 3,800 pound boat to the keys and back 10 times. I didn't realize I was overloading its tow capacity until after I sold it and was looking for another truck. I never burned out the PCM in my 1990. In 197,000 miles the only thing I replaced twice were headlight bulbs and front brakes. I bought it new and took good care of it - it lived most of its life in a barn, rarely sitting outside [until my divorce, where I lost the house, barn, acreage...]. I escaped with the truck, boat, dogs and my life.