Red Wrench

The wrench is the placement tool and the Wire in your inventory is what it spends, the same way a bow spends arrows. Buy it from the Mechanic after you have rescued her from the dungeon. Red is one of four available colors, and the only thing the color of the tool decides is the color of the line it lays down. Once placed, every color behaves identically.

Different colors let two separate circuits share the same tiles without setting each other off. Build your door system in red and your lighting in blue and they can run down the same corridor with no interference, which is the whole reason to own more than one wrench.

When two lines of the same color genuinely have to cross, a Junction Box keeps them apart at the intersection. And there is no penalty for choosing badly: pulling wire back up always returns the same generic wire item regardless of what color it was on the wall.

A wrench cannot take wire out, only put it in. Removal needs a Wire Cutter, so carry both if you are working on something you expect to revise.

Once you own all four colors they combine into the Multicolor Wrench, which handles every color from one slot. After that the singles are only worth keeping for multiplayer, where giving each person a different color keeps everyone's work identifiable on a shared build.

Holding a wrench draws every wire on screen, including the lines feeding dart traps and boulders in dungeon and temple corridors you have not walked yet. That alone earns it a hotbar slot while exploring, well before you have any interest in building circuits. Holding one also extends how far you can reach to place and interact with tiles.

Smart cursor changes what the tool does, which is worth knowing before it surprises you. With it on, the wrench extends existing wire of the same color rather than starting a fresh run. That is exactly right for long straight lines across a base and exactly wrong when you are threading a tight circuit next to wiring you do not want to touch.