1990 E250 4.9L six cyl with A/C Serpentine belt diagram

SOURCE: 1995 buick rivera serpentine belt install?

look around under the hood , on the underside of the hood, sometimes the belt routing diagram is on a sticker also check a Chiltons Manual sold at auto pARTS STOReS or on the web

SOURCE: 1987 Buick Century 2.5 serpentine belt diagram

call a parts store they usually can provide you the routing for serpantine belts good luck getting it right though it can be tricky pay close attention to how the belt is routed :)

SOURCE: diagram for 1998 buick lasabre serpentine belt

I found the diagram in my owner's manual.
I replaced the belt on mine just 2 days ago. All you need to do is remove one bolt from the lower motor mount and remove the spacer. After you relieve the belt tensioner, the belt will slip right through the gap. Don't forget to support the engine before removing the bolt. As a backup I took a photo of the belt with my digital camera beforehand... just in case.

SOURCE: serpentine belt diagram for 2003 buick le sabre

Since there is NO sticker under the hood of this 2003 Buick LeSabre and it is not in the owner's manual, a Google search revealed that it is the same as at http://www.fixya.com/cars/t3438653-change_serpentine_belt_1998_buick