The upper engine harness is the most susceptible to disintegration due to its proximity to the hottest parts of the engine. I've been told many times not to worry about the lower one (and yes, it is a LOT more expensive...)
Now that you mention problems occurring after washing the car, I do recall that something similar happens to me, although it hasn't been too much of a problem for me to tackle it with the same gusto. Everytime it rains, or when the car is washed, (1) the antenna refuses to retract and (2) the passenger side fog lamp dies, triggering the dashlight telling me of a burnt out bulb.
Then there's also this weird problem of some (not all) of the dash and switch lights coming on (a/c vents adjuster, gear selector, rear sun screen, seat heaters etc). It goes away after driving for a while (I could almost swear it goes out after mashing the go pedal in gear but I'm not sure). It only happens when you don't use the vehicle for days. What worries me though is that the lights are on when I get in the car so it can potentially drain the battery.
I know that's not quite helpful but in situations like this, seemingly unrelated symptoms might point to the solution.
Best of luck.