In this video, we cover how to splice thermostat or control wire with a lineman's splice, also known as a Western Union Splice or NASA splice, using a soldering iron and heat shrink.We often see substandard splices on low-voltage wires; you may see a splice consisting of a ball of wire nuts and electrical tape. Lineman's splices work well for underground low-voltage wires when rewiring isn't practical. These splices work well because they are tight, can handle a lot of tension, and won't corrode over time.A lineman's splice requires us to cut out the source of the short and strip the wire back. Make sure you pull the casing back far enough to have plenty of room to work with the wires. We cut off the loose casing AND the wire tips. You'll want to splice every single wire, even if you don't think you'll use them all, because someone may need to use those wires later.When splicing one conductor, we only need 1 1/2" of heat shrink, so you may choose to cut the heat shrink if it's too long. (Half-inch heat shrink works for the outside jacket, and 1/8" heat shrink works for the inside conductors.) Fit the heat shrink over the wire BEFORE you solder the splice; otherwise, you won't be able to get the heat shrink on. Keep the heat shrink AWAY from the splice as you solder it, as the heat can make it shrink down.Once you've created a connection by twisting the wires, you can solder the conductors. Once you've soldered the connection, you can slide the heat shrink over the splice. Before you apply the heat, make sure there aren't any bare wires. It's best to have at least 6-8" of wire on each side for the splice to be practical.Note: Do NOT use this splice without soldering it.