A relay isn't shown or mentioned, but I doubt that cheezy switch can handle 10A, so I bet there's one in the box. The stock eB fuel gauge switch was built before they knew how to make reliable low-current switches, but I still don't think it'll stand up to 10A, even if you double-wire it. A relay is cheap & easy, so I'd use one in any case. Use this as a guide, but use a modern Bosch/Tyco cube relay. Start with a 15A fuse near the battery going to relay terminal 30; run the switch from a stock circuit that's powered when you want (park lights, ICVR, whatever you choose) to 85; 86 goes to ground; 87 feeds the lights.
That shows an illuminated switch, which is the reason for the extra ground at the top - you'll only use a center terminal & one other on that side.