1954 Chevrolet trucks were all 6v systems.

An alternator is an indicator that changes have been made, most likely to 12v, but there is very small chance it is a 6v alternator.

If the battery has 3 cells (caps), it is 6v; if it has 6 cells (caps), it is 12v. 8v batteries were a rare "upgrade".

Post a few of the light bulb numbers and they can be identified as 12v or 6v.