There's no need to switch the power wire feeding the inverter. Every inverter I've installed has a simple "ON/OFF" toggle mounted on it and all you need to do is remove the cover to the inverter, access the red and black wires coming off the back of the toggle switch, and tap into those wires with an ignition-switched relay or a dash mounted toggle, depending on whether or not you want it to work only with the key. With my wife's DD, a minivan, I was concerned about the inverter being left ON so I went the relay route. In the cargo area, however, I installed a Dayton spring-wound 30-minute timer next to the outlet and ran the wires from that up to the connections I made with the relay. Now, 99% of the time the inverter works only with the key but when we go camping and I want access to 110vac without digging for my keys I simply give the timer a quick spin and I have 30-minutes of use without worry that if I walk away my battery will be drained.
~ 1995 ZJ
~ 2.25" BB
~ Rough Country Nitro 9000 shocks
~ 31x10.5x15 Dunlop Radial Mud Rovers
~ 15x8 black Unique wheels