Headlight relay

I have one on my Hornet that was purchased from Fifth Ave Auto Parts in Kansas for about  $35 and comes with instructions. Basically  it  is wired through the dimmer switch and from the battery "hot" wire with a fused circuit. Can't beat it .

Here is a diagram I used for a 6 volt relay

What's the main advantage of retrofitting headlight relays? Is it to keep from running all that amperage up under the dash and back?

Just FYI, the max draw of two 12v H6024 headlamps is 10 amp, so I don't believe you need such big fuses or separate relays.  A 15-20 amp relay/fuse system will more than suffice for headlights only.  That's the beauty of doubling to 12V!  A 6V system may require double the amps, wire thickness, and fuse capacity.  If you are re-doing a whole bunch of wiring consider a modern 12V system under the dash.  Either way, 60 yr old wiring carrying all this current scares me.

Here is one of my post from a few years ago.  I did a relay and also halogen insert bulbs.  You can see the difference.  Not afraid to drive at night after this.

The big advantage of q-h bulbs is the extra lumens from the same wattage.   My 1928 Essex still has its original steel sheathed wiring, and the  headlamp switch used to get so hot the  solder in the fuse would melt occasionally.  The problem was that originally the bulbs were only 24 watt, and  you can only get 36 watt these days, so the extra current was too much for the old circuitry.  I  upgraded the charging system by fitting a later model (post war)  2-brush generator and voltage regulator, which fitted straight in to the Essex cradle.  How's that for interchangability?  All I had to do was weld the drive collar on to the front nut of the generator.   I then installed a wire direct from the bulb holder to the chassis for good ground circuit,  fitted a relay right up by the radiator, and  q-h bulbs.   These lights are fantastic, and still using 6 volts and 87 year-old wiring.  Now when driving at night, with the lights on low beam, I let the oncoming traffic flick their lights at me twice, then I give them head beam full bore!   Only down side (if you could call it that) is that you no longer get a net reading on the ammeter, as the supply for the headlamps now comes direct from the  battery terminal on the starter.   So now  instead of showing about 2 amps charge when driving with the headlamps on  (before fitting the relay), it shows 15 amps.   Enough wittering!