So you have lost dip/main, but flash works main beam ?
Get your metre out and test for OUTPUT from switch on dip and main when turned on to headlights.
These swithes are very often burning out the switch contacts, this is the most likely cause, so try this first.
If the flash is working it shows the main beam circuit is good, the flash live eminates from a different source, as it is live irrespective of light position, and will be the one that also supplies the feed to your horn button.
tabetha