Is a 1999 Pontiac grand am power window switch compatible with 1998 switch?

It's highly likely, but not guaranteed. While 1998 and 1999 Pontiac Grand Ams are very similar, there's a small chance of minor differences in the wiring harnesses or switch design.

To be sure, you should:

* Check the part numbers: Find the part number on both switches. Identical part numbers mean they're interchangeable.

* Compare the connectors: Visually inspect the connectors on both switches. They need to be identical in size and shape.

If the part numbers match or the connectors are identical, they are almost certainly compatible. If there's any doubt, a parts store (auto parts store or online retailer) that has access to parts diagrams for both years can confirm compatibility.