Hello folks, sorry to bring in some counter points to the general consensus here but YOU DONT NEED RELAYS. In my opinion there is entirely too much use of relays in the LBC world. People get them misused, misinstalled, poorly grounded, etc, etc and then they have more trouble and alot of spagetti wires all over the place. Generally the running lights used as Fog or Driving lights such as the Lucas ones seen in Moss HAVE NO MORE THAN 60WATTS. On 12 volts that equates to 5 amps each so 10 amps for the circuit at best. You don't need a relay for 10 amps. Use a piece of 14 or 12 gauge stranded wire and it will handle 10 amps easily. Some say well you are protecting the small switch with a relay. I have been running my fuel pumps, driving lights and OD on 20amp toggle switches for years with no problems. Now as to your source of power. Just as a side bar, I have an 8 pole fuse block installed under my dash above my foot pedals which provides me with many points to pull another fused circuit if I want to but, If you are running the original 2 fuse fuse holder out on your firewall then know that the bottom fuse is the largest at 50 amps and it is almost doing nothing. Most of all the cars electrics are run off the top fuse which is a 35 amp fuse. the bottom 50 amp fuse was designed to be used for accessories such as radio, cigarette lighter, horns and of all things RUNNING LAMPS. If you have an early 100/6 the 50amp bottom fuse has two brown/green wires on one side of it. These go to the horns. If you have a later car you probably have just one wire on that side of the 50 amp fuse and the one wire goes to both the horns. I should be purple. But here's the deal, that fuse is fed by a brown wire. That brown wire comes directly off the "A" terminal of the voltage regulator which is fed directly from the battery terminal at the starter solenoid. You can't get much cleaner power than that. But too on that same era of Healey, the 100/6, the head light switch is powered directly off the A1 terminal of the voltage regulator with a brown/blue wire. But i would stay away from the headlight switch because it already is loaded up with a lot of current and I would not add another 10 amps to it. So the easiest way and one that will be trouble free by the KISS method (keep it simple stu...) is to attach a 14 or 12 guage stranded wire to the load side of the 50a fuse and run it to a 20amp toggle switch and then to the lights. Bingo, done. If you feel that the 50amp fuse already has too much on it, example being, horns, radio, etc. then you could attach your source wire to the feed side of the 50 amp fuse and use a 10amp inline fuse holder to fuse your new wire. Or the most direct source from the battery is the "A" terminal of the voltage regulator. Put your source wire on there with an inline fuse hold and a 10 amp fuse. In the pic of my fuse box you might notice that the only 10 amp fuse I have is on the OD. This has been working this way for years and I have no relays in my car.