Either the fuse box or the ign switch, whichever is closer to your gages. At the fuse box, you can get taps that slip over the round fuse and let you attach a spade lug. At the ign switch, if you don't want to cut your factory wires, you can do like me and remove the "56 terminal" from the connector (use thin screwdriver) and insert a new wire that goes to a junction where you plug in your existing wire. I ran it to a 40 A relay coil (wired base) so the ign switch doesn't carry the ACC current (good idea, not essential).