Jerry's drawing is great, but needs a fuse or (preferably) a self resetting circuit breaker as near as possible to the source for the battery voltage. My truck has no ammeter so I attach my headlight wire to the battery stud on the stomp starter switch. Then mine runs about 1 foot to the firewall mounted circuit breaker and then up to the relays that are mounted near the old left inner fender front lights terminal block used to be. Use 12 gauge wire for this connection.

Finding a circuit breaker specifically rated for 6v is hard to do, but there are a number of them rated for 6-28 volts. Typical 6 volt high beam current draw is around 7 amps (40 watts) plus 7 for the passenger's side so a 20 amp circuit breaker should do the job.

'57 GMC 102, Original 347 V8, HydraMatic, 3.08 rear gear, added A/C, disk front brakes, HEI, AFB carb, '98 Honda Black Currant paint. T-boned and totaled 10/12
'52 GMC 152 Stake Bed, Original 228, SM420, added A/C, HEI, disk front brakes, '67 Chev 3.55 rear gear. Gets used as a real truck.