If you have an original type wiring setup, radios are usually connected to either the ammeter on the load side, or at the non-switched side of the ignition switch. An inline fuse would normally be used for a radio. This arrangement means that the radio is not turned off by the ignition switch.
If your radio is 6V and your truck is 12 v, you will need some kind of reducer. A voltage reducer will get pretty hot so you would need to allow for the heat.
