Diagram for serpentine belt 88 deville serpentine belt?

Most replacement belts have a diagram on the package. However, the easiest way is to pay close attention to the belt you are taking off, and replace the new one the same way. The pulleys themselves...

As you listed no make, model, engine, or year, all I can say is look under the hood for a placard diagram. Usually there is one there.

where can i get a diagram for a serpentine tensioner belt for a 1998 Oldsmobile bravada

If the alternator belt is the same belt as the other accessories, yes.

If you go towww.autovalue.com and look up the belt for your car, you can click on the first line in the parts list and get a routing illustration to print off.