2001 Toyota Sequoia horn works sometimes. I changed the fuse. Is it possible that the relay is bad? How would I know?
You will have to test the system logically :
1 supply - is it intermittent
2 switch for operation
3 supply to relay
5 supply to horn
7 earthing of horn but you can do this first as it is a common issue.
For testing use a test lamp or multimeter : lamp probably better in this case as it gives a more "visual" response when power is there...