Question: I’m trying to trace some DC wiring on my boat and find myself lost in a sea of red (see photo). I’ve read that red is pretty much universal for DC positive conductors, but on my boat there are a lot of circuits, and that seems to mean a lot of red wires. It’s easy to figure out what’s what at the switch end of everything because the switches are all labeled, but when I try to trace through the large bundle of red you see here it’s easy to lose track of which wire is which. Any thoughts or suggestions on how to deal with this?
Answer: Well I have several thoughts and a suggestion. You are quite right that red is pretty much considered to be the universal wire insulation color for DC positive conductors. But in your case you're dealing with quite a few red wires, so a conscientious boatbuilder would go to the next level and find a way to further ID each wire as to its specific use. There are several ways to do this: one uses heat-shrink tubing with circuit names shrunk onto the individual conductors; others simply use circuit numbers and follow up with a nice decoder chart that tells you what wire number 87 (as an example) actually does.
But even with that consideration, heat-shrink labels typically only appear at either end of the wire in question. On a lot of boats the wire runs are long enough that tracing the individual wires down their length will still be challenging. So, what to do? Get yourself a wire-tracing signal generator, sometimes referred to as a “fox and hound” set-up. The rig I use is made by Fluke, and I actually picked it up at the local home repair big box store in their electrical department. The cost was about $90, and it really works quite well. (See photo.)
To use the fox and hound you need to have two conductors that run parallel to one another down the wire run in question. Using the signal transmitter, you clip on to one end of each of the two wires and turn the unit on. Now you can follow down the wire run or simply go to what you believe or know to be the far end of the cable run and with the handheld wand touch the individual red wires until you hear the generated tone, which will be a rather loud beeping noise. The beep will be loudest by a significant margin when you actually come in contact with the wire the signal generator is connected to. You can track this wire down the entire length of the cable run as long as you have access to the wiring on your boat. The tool doesn’t do a very good job of tracing wires hidden behind panels and cabinetry in my experience, but you sure can single out individual conductors at either end of the cable run with it.