Very sorry that I screwed up, ... Again. I looked up the brake light switch and found that they are still using the same miserable switch they had in the '70s. It does not have a power circuit built in for the cruise control like every other manufacturer uses. For your cruise cutout switch, two different switches are shown. One is located on the master cylinder, and one looks like it would be right behind the brake pedal, possibly with a connecting link, but that isn't shown.
So, to answer your original question, the brake light switch appears to have nothing to do with the cruise control except to provide the "cancel" signal when you tap the brake pedal. The switch on the master cylinder is a backup cutout switch in case the main one doesn't work. It DOES get its power through the brake light fuse like all other manufacturers do. That is so the cruise will not work if the fuse is blown because with that blown fuse you would also never get that cancel signal.
So to clear up my story, if the brake light switch was defective, the cruise control would still set but it would not cancel. If the secondary switch on the master cylinder was defective, the cruise would not set. Is it possible your mechanic was referring to the switch on the master cylinder?
The only service manual I have is for '96 models but they use the same switches as the '03s and '05s so the circuit should be the same. The wire colors might be different on your van, but my book only shows two of them, a light green / red and a red / light green. Both of them should have full battery voltage until you press the brake pedal, then the red / light green should go to 0 volts.
If voltage is missing to both wires, check if the brake lights work. If they do not, check the brake light fuse. There is another fuse shown in the interior fuse panel for just the cruise control. It is a 20 amp fuse.
If both fuses and both switches are okay, the most likely suspect would be the clock spring coming apart. That is a wound-up ribbon cable in a plastic housing under the steering wheel. It's a fairly high-failure item. As it continues to break, eventually the horn will stop working and the air bag light will turn on.
Sorry for taking so long to reply. The site stopped working on my regular computer so I'm borrowing a miserable laptop.
Saturday, May 21st, 2011 AT 5:59 AM