The 2 fuses on '50 - '54 trucks were for the wiring going "out back". One for stop lights, and one for tail lights.
The Shop Manual for '48 - '51 trucks does indeed show a 5 slot fuse panel and cover for the '48 - '49 models. These were for:
1. High beam
2. Low beam
3. Park
4. Tail lights
5. Stop lights
