Peter, you're confusing terminology. Within the context of our discussion, a "fuse" is an electrical safety device that permanently interrupts current flow through a conductor (wire or circuit) if current flow through the circuit becomes excessive (greater than the amperage rating of the fuse). Fuses effectively protect circuitry from damage by melting, severing electrical connection, before other circuit components can overheat and catch fire. Fuses fail catastrophically, meaning that they cannot recover after melting and terminating current flow. The roughly 1" long clear glass capsules with metal end caps in the fuse box image you posted are "glass" fuses.
The metal can in the top left corner of the fuse box is called a "flasher." It is a very specialized type of automatically resetting circuit breaker or thermal relay. It functions as a switch that cyclically turns the signal lights on-off-on-off-on-off... as long as power is applied through it. The hazard and turn signal flashers are interchangeable.
Looking at factory wiring manuals, the 1976 and 1977 C & K models had the turn
and hazard flashers located in the fuse box (hazard flasher at top left and turn flasher at lower left). But, according to the
1978 Wiring Manual, the C & K models of that year used a "divorced turn signal flasher" that dangled out of the harness as I previously described. Generally, divorced flasher fuse boxes did not incorporate the two terminals for the turn signal flasher - there were no socket holes in the fuse box for the turn flasher.
The fuse box in your truck, however, was manufactured to physically accommodate a turn signal flasher. From recollection, there were very short transition periods during production runs in which 'divorced flashers' were used even though the fuse box was manufactured to accommodate both flashers. In those cases the turn signal flasher terminals were missing from the fuse box - the socket holes were there as in prior years, but they were blank.
Regarding your truck, if a free hanging flasher socket is absent from under the dash and the flasher terminals are missing from the fuse box, I would inspect the backside of the fuse box to determine whether you can just install the appropriate wires and mount the turn flasher in the box using Packard 56 series terminals. Of course, there is still the matter of finding the existing wires under the dash (dark blue is ignition power into the flasher, purple is power out to the turn signal switch).
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