1992 sonoma tbi issue

I am having an issue where my right injector is spraying but the left is not. However
When I switch the harnesses it is the opposite. The left sprays and right
Doesn't. My question is what are some of the possible causes. Im not sure if a relay or wire or what exactly to search for. Thanks for any help

Each injecor may have its own fuse, should be a three or five amp fuse.