I've checked all the fuses. Without having to follow the wiring, does anyone have any advice on what the issue maybe?
Checked all the fuses with a meter? Is there good power/ground at each?
Welcome to HEF JJBacon ! Machine serial number? These would most likely be two separate issues. F20 fuse is the one to check for the horn. Serial number determines whether a fuse is in the circuit or not for the backup alarm.