Somebody above mentioned "60 Watt". Watts and amps are not the same. Big wires and relays are just a common sense upgrade for most of the old rigs we work on. Material cost is a one time expense- - - -voltage drop and dim headlights as a result are forever. Mount the relays on the radiator core support as close as possible to the headlights, and run a voltage supply wire with 8 or 10 gauge wire to power the relays. Run a self-resetting circuit breaker (NOT A FUSE) on that wire. In case of a short, the lights will cycle on and off as the breaker resets, not go out altogether from a blown fuse.
Jerry