90 Horn Fuse Location
I have a 1992 Corvette & I think they are the same as your 1990. It is fuse location #7 and is a 15 amp fuse. Fuse box location is on the passenger side when you open the door you can gain access.
Search Chevrolet Corvette Questions
Are you a UK consumer? CarGurus now has a discussion forum in the UK.
Chevrolet Corvette Experts