Welcome to iRV2.
Sorry your first post is about problems.
The possibility of internal problems with the multi function switch can't be overlooked .
You say the fuse blows as soon as the ; ignition switch is turned on .
Was the wiper switch in the off position ?
Do you have a chassis owners manual , that would tell you if the fuse that blows ONLY supplies power to the wiper system ?
Have you disconnected the multi function switch wiring at the base of the steering column to see if that stops the fuse from blowing?
Do you have a 12 volt test light ?
Wiring a 12 volt test light , in place of the fuse , will save on fuse replacement till you pinpoint your problem. The bulb in the test light acts as the system load , when the bulb is lit you still have a grounded circuit.
The image below is from a search of a Workhorse multi function switch .
Does the wiring in the image match what you see on your steering column?