I agree with BMRFIXIT. I replaced dozens of switches for the exact same symptoms, ... And I was not even one of the electrical specialists at the dealership.
By the way, it's nice for a change to speak with a fellow electrical expert!
There are a number of different circuits controlled by the switch so some things might work while others will not. Sometimes problems don't show up until the engine is running because the charging system raises system voltage which results in more current flow through the switch circuits. More current means more heat buildup in the contacts. Engine and road vibration aggravate the problem. Normally I would suggest wiggling the switch when the problem occurs, but since you already replaced it, did you happen to look at the connector? Sometimes a terminal in the connector overheats and becomes discolored or even turns black. In that case, cut the melted plastic plug apart, splice in a good clean piece of wire and solder on a new terminal. (Don't just crimp it to the wire).
You might check for a connector near the base of the steering column although I don't recall ever finding a problem there.
The next most likely thing to check, if the new switch didn't help, is for a loose fuse behind the brake pedal. I left the dealership in late '99 but I doubt the design changed very much after that. It was pretty common for fuses to fall out onto a customer's ankle while they were driving. To save time, we just put a slight twist in the blades of the fuse and reinstalled it.
By the way, it was a NEW switch, right? 45 bucks seems kinda low but maybe the price has come down. Full size trucks have had so much trouble that there's a factory fix that involves installing a harness with a relay to handle the high current.
As a point of interest, there is a service bulletin for the cassette player changing direction when both power windows are rolled down. It doesn't really change direction, it just sounds like it does. Caused by increased current when both window motors stop moving. That results in higher voltage drop across ignition switch contacts, lower voltage to the radio which thinks the switch was turned off so it retracts the head and pinch roller. Release power window switches and the cassette player starts working again.
Anyhow, if none of this pans out, holler back and I'll dig out a service manual and check the diagram.
Tuesday, March 17th, 2009 AT 7:48 PM