I have part of the answer. On the 1998 Sienna (same as th 2003) there are 2 light assemblies; one is in the liftgate and the other is in the body of the van.
Today I just replaced the brake lamp in the light assembly in the body. To do this operation all you need is a 10mm socket. Remove the 2 retaining screws (visible near the inside edge of the lamp assembly, open the tailgate to see them.) Once you have removed these 2 screws, grab the lamp at the inside edge (near where the screws were) and pull back and out. You will be afraid of breaking the lamp assempby, but don't worry, it will come free. Not visible until the lamp is off are 2 large pins located at the leading edge of the lamp which are inserted into rubber sockets in the body - they worh in a snap-on / snap-off manner. The lamp assembly will pop free with some forcefull pulling. Installation is reverce of removal.
The 2003 Toyota Sienna has 24 valves.
The 2003 Toyota Sienna has a V6 engine.
The 2003 Toyota Sienna is a gas-powered vehicle.
The 2003 Toyota Sienna has a 4-speed automatic.
The curb weight of the 2003 Toyota Sienna is 3919 lbs..
The 2003 Toyota Sienna has double overhead cam (DOHC).
The height of the 2003 Toyota Sienna is 5 ft. 7.3 in. (67.3 in.).
The 2003 Toyota Sienna is 16 ft. 2.2 in. (194.2 in.) long.
The 2003 Toyota Sienna has a drag coefficient of .32 Cd.
The 2003 Toyota Sienna runs on regular unleaded.
The maximum payload of the 2003 Toyota Sienna is 1327 lbs..
The 2003 Toyota Sienna's turning circle is 40 ft..