After determining the multifunction switch in my 98 ranger is faulty, I searched for switches and found p/n ARBM505801 and ARBM505802. Does anybody know the difference between the two, other than $8 price difference?

 

The part number being different doesn't always mean there's a difference that the end user will notice.

Say, for example, a company has a product with a part number 1234. People buy the product, but complaints roll in of one of the pieces breaking too easily under normal wear. Their design team decides to make the part that's breaking out of a different material that's stronger. The new product is numbered 1235. Both products work the same way, look the same way, but 1235 has a few minor improvements that 1234 doesn't.

Given the increase by 1 on the part numbers you have, I would venture to say that is the case here.

What I would do though is go to rockauto, find your year model and engine in the list, find the multifunctions they have listed and compare part numbers. Buy which part number they list for yours.