US based LHD Valiant?
IF so, you can download an FSM with the wiring diagrams.
use them to make a schematic.
Horn is powered through a relay.
The steering column switch trips the relay. The relay connects the battery to the horns.
1967 Relay connects horns to battery from the output stud on the alternator. No fuse.
1968 might be there, or they might have moved it.
Emergency Flashers (hazzards) and Turn signals: Each uses their own flasher.
Hazzards & Stop lights get the positive power from a fuse that is always hot.
Turn signal gets power only when key switch is in run or accessory position. No fuse, at least in '67.
See if there is power to the turn signal flasher with key on.
The flashers are bimetalic strips that move when heated by current flowing through them. no current flow, no heat, no flashing.
