Fuse Box cover for hardwire kit ?

[CrankyOldMan]

Our version of Princess Auto or Canadian Tire sometimes has coupons for a free tool (flashlight, screwdrivers, multimeter, etc.) in their flyer.

Correct, the negative terminal on the battery or any bare metal should be the "ground" potential. There's no ground reference inside the fuse box, typically it's a local point on the chassis that looks like a beverage can tab screwed to the metal. Toyota's ground wires are usually white with a black stripe or just brown.

The large black or white wires bolted to the side of the fuse box are live from the battery and provide power to all of the fuses. Even the empty fuse slots can be used with a fuse tap, just make sure you have it oriented correctly and the power goes through the fuse in the tap, not directly to the tap wire.