Where is number 1 on the distributor cap of a 5.7 1989 Chevy 2500 pickup?

On a 1989 Chevy 2500 pickup with a 5.7L engine (a small-block Chevy V8), number 1 cylinder is typically located on the passenger side, and the number 1 wire on the distributor cap will be at the front.

However, it's crucial to verify this. There's no guarantee without physically checking the engine. The distributor cap itself may have the firing order marked on it, and the engine block itself will often have a casting marking to help identify cylinder 1. A repair manual specific to your truck's year and engine is the best resource for absolute certainty.