Sounds like the problem is with the ignition switch harness Part # 26068757 When your fan starts working intermittently on speeds 1-4, and eventually only works on the highest speed, this is the part that needs to be replaced. Goes from the steering column down to a large terminal block. Its almost 2 feet long and looks like a huge wire harness with big black connectors on each end.
Here is what ive found.
Once and for all I figured out the real reason behind the DRL-DIC-Fan problem. From what Ive read at clubGP it got me looking in the right area, the ignition switch. So first a big THANKS goes to everyone who said that harness fixed their problem.
All of these things get power through the ignition switch, specifically the RUN terminal (when the key is in the 'RUN'position), which is an orange wire on the bottom of the switch. When the problem was occurring I was getting fluctuating voltage on the RUN terminal (measured with a multimeter), jumping anywhere from .5 to 10, but usually hanging around 1 or less. When it was working properly the voltage read normal battery voltage, 14 or so. When the problem was occurring and I jumped that terminal to an always hot terminal everything came on and worked perfectly. So great, it's something in the switch.
Being the curious type I took the switch apart, figuring at worst I'd have to buy a new one... Would you believe the problem is carbon buildup a little larger in size than a pinhead? It's actually kind of nifty how they made this switch. When you turn the ignition key it turns a spring loaded plastic shaft in the switch. On this shaft are 6 lobes sort of like a camshaft, though not as tall. Each lobe has a rocker-shaped piece of metal spring loaded to rest on the lobe. As the shaft is turned when you turn the key it causes the various rockers to move out due to the lobes and make connections with terminals laid out by either side of the shaft. So, turn the key to RUN and the shaft turns moving the rocker out to make connection with the RUN terminal.
The beauty of this mechanism is how it can turn on or off certain terminals depending on how far the key is turned. An example of this is when you turn the key from RUN to START. The lights and fan go off because the RUN rocker is coming back down off the other side of the lobe as the START rocker goes up and makes its connection to send voltage to the starter relay.
It is this on-off-on action of the RUN rocker every time you start the car that I believe causes the problem. At the point where the rocker makes the connection to the terminal some arcing is taking place due to the volts and amps being drawn, causing a carbon buildup at that point. The more carbon that gets built up the worse the connection gets. Since the fan draws its voltage through this terminal more arcing is taking place if the fan is running when you turn the key. As a result there is more carbon buildup as compared to the other rockers that had very little or none at all since they do not have such high voltage/high amp devices to feed. I cleaned off the carbon with a soft wire brush and juggled around the rockers so the relatively 'unused'ones found themselves switched with the 'overused'ones.
I have not had a problem since then. Since the fan is probably the biggest contributor to the arcing and resultant buildup I am making a point of it to have the fan off when I turn the car on or off. This should help keep this problem from coming back for a great while longer.