Sooner or later, you’ll want to add some new equipment or a new accessory to your RV. The same techniques can generally be used for fifth wheels, motor homes, campers, and slide-ins. Also, generally speaking, it really doesn’t matter whether you’re running 12-volt power lines, speaker wires, coax, computer wire, or lighting.
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For the purposes of this article, we’ll discuss running and hooking up 12-volt power wire. That way you get to learn about running wire in your RV and get some extra 12-volt power information.
First, you have to identify and locate your 12-volt power sources. Most RVs have batteries located in or just outside the coach, cabin, or living area. The battery supply might be one or more 12-volt batteries, or two or more 6-volt batteries wired to provide 12-volts. Where possible, and if desirable, you can connect your new power lines directly to the batteries.
You may also have solar panels which are designed to put out 12-volts, BUT these are designed to charge your batteries, not to power things directly. That’s because batteries are built to supply large power loads, and solar panels are not.
RV Wiring Basics
Remember, if you’re connecting directly to the battery, make sure you put an inline fuse on the positive (hot or +) lead, and that it’s some place you’ll be able to reach and change it if needed.
If you trace your existing wire routing, especially in bigger or updated RVs, there’s a good chance you’ll find a power bus or distribution bus. They usually look like a bunch of bolts in a line with nuts and washers to hold wires in place. A distribution bus can also be an excellent point to tap into for 12-volt wire, especially if it’s already fused – if not, add a fuse.
If the RV location you’re trying to get 12-volt power to is close to an existing circuit nearby, you may be able to tap into it. This makes a lot of sense for low power devices such as LED lights or a charger for a cell phone. Even if it’s a low power device, it’s still a good idea to trace the circuit so you know the size of the fuse protecting it.
Enough of the 12-volt RV specifics. Now, let’s talk about getting a length of wire from point A in your RV to point B.
ou’ll be choosing from two wiring scenarios and you’ll have three options. You’ll either be running wire from the outside of your RV to the inside, or inside to inside (technically, you could be doing outside to outside but that’s usually as simple as laying out a wire and securing it.
THE MOST IMPORTANT RV WIRING TIP YOU’LL EVER READ!
Whenever you run a wire, also run at least one string with it. That way, after you’ve successfully run a wire in your RV, you have an easy way to run another one in the future. Make sure you run a string with that future wire as well.
When you’re routing wire from the exterior of your RV to the interior, look for anything else that’s already running from the inside to outside, or all the way through the living area of your RV. A good example is taking a wire from the roof down to the bottom of your motorhome or fifth wheel. There are already tank vents that run from the top of your unit to the bottom and you can usually drop a wire alongside them. Just make sure you’re not dropping a wire INTO your black water holding tank. You can usually figure out which interior wall or bulkhead of your RV the vent pipe is running though. You can then remove a cover panel, make a hole and cover panel, or make a hole and patch it to fish the wire into the interior of your RV.
Similar to the vent pipe, you can also find a fridge vent for refrigerators that run on LP (propane). This runs from the roof to the interior.
If there are no available openings, you’ll have to make one. Obviously. You want to avoid a wire coming through your roof and end up dangling from your ceiling, so try to line up your exterior opening with an interior wall, inside of a cabinet, under a bench or bed, etc.
Rather than drilling a hole and schmucking a big, messy glob of sealant around it, you can create a weather-proof entry port. The easiest way is with an exterior-rated PVC electrical box. These have multiple threaded openings that can be capped or have lengths of exterior-rated PVC conduit attached to. The back of the box may already have a hole in the back but, if not, drill one to match the size of the hole on the exterior of your RV. Place a healthy amount of sealant (appropriate for the exterior of your RV) around the hole and place the PVC box on top of it and then fasten it with the appropriate screws.
Add a short – about 4-inch – length of PVC conduit to the hole you’ll be using to get your wire into the PVC box. Now, route your wire from the exterior, through the short piece of conduit, into the box, and then down the hole to its destination. Alternately, you can run a wire from the exterior to the box, and another wire from the box to the final location, and then connect them with electrical wiring nuts / connectors. When the above has been done, shoot some silicone sealant into both ends of the short piece of conduit. Using silicone lets you pull out the wire later if needed. Then screw on the matching PVC coverplate. If the box or cover plate doesn’t include a seal of some sort, use a small bead of silicone or caulking before putting the lid on. Screw the lid down to the box.
The big advantage to creating an entry port like the one above is that you can easily add more wires later, simply by uncapping one of the other access holes.
Whenever you penetrate the exterior of your RV, make sure you seal it well with sealants that match the exterior material of your RV.
Running wire from Point A to Point B on the inside of your RV can actually be more difficult than outside to inside – depending on where the two points are located. Every motorhome, fifth wheel, slide in, or camper is different… and there are dozens of reasons for running a wire… so each situation will be different. Following are a bunch of RV wire routing tips.
Run wires in the back of your RV cabinets. The least obtrusive way is to drill a hole (or holes) in the top back corner of the cabinet(s). That way your wire is as high as possible and all the way at the back – so it doesn’t interfere with your storage.
If you have ducted air conditioning, you can run wire through the ducts. However, you will still need to create an entry and exit hole somewhere in the ducts. If the ducting is metal, watch out for sharp edges at the entry and exit points and anywhere along the wire run. NEVER run wiring through the heating ducts. It’s unlikely the temperature would get hot enough to melt the wires, but it IS possible – and it only takes a small short circuit to create a big fire.
Exterior wall are usually not hollow since they’re insulated. Interior RV walls are usually hollow and generally have framing (supports) running vertically. To check for framing locations, a standard stud finder should work. Be aware that even a hollow interior wall can hold surprises including, but not limited to, existing wires, plumbing pipes, cross-bracing, pocket doors, etc.
For major wiring projects, or those gotta-have-it and there’s no other way wire routings, you might have to make multiple holes in a wall to fish the wire. In that case, just do it and look at it as an opportunity to repaint or repaper that wall.
Look for anything else that’s already running the entire route, or parts of it. For example, the holes drilled for your existing plumbing will probably be big enough to run a wire through them as well. If the holes are sealed, remove the sealant, run the wire, and reseal it.
Sometimes the best inside to inside wiring route for you RV is actually inside to outside to inside. For example, you may be able to drop into an exterior storage compartment, run the wire under your RV, and the pop up inside that dinette bench you want to add that USB power outlet to. Again, whenever you’re crossing the RV exterior interior barrier, seal the hole.
Consider running an exterior grade conduit, pipe, or hose instead of the wire – especially for long runs. Then run the required wire through it. This will make it easier to run future wire that can take advantage of the same route. Also, an exterior cover will protect your wires from road damage, weather, and rodents.
Unfortunately, due to the pesky laws of physics, it’s not always possible to run RV wires inside wall, under the floor, or behind cabinets. In those cases – or if you just don’t feel confident drilling and cutting holes in your RV – you can use surface wiring.
Obviously you don’t want lengths of wire hanging around looking ugly and becoming a hazard. Fortunately you have two neat, clean, and easy RV surface wire routing options. The first and simplest is surface mount wire channels or conduits. These typically have a flat surface that goes against the wall or ceiling, a space for your wires, and a removable cover. Many are self-adhesive, with a peel-and-stick backing. Depending on the surface you’re mounting them to, and the quality of the adhesive, you may want to use an adhesive of your own, or use small screws through the backing for extra support. My advice is to go with the supplied adhesive and see how it works. No sense creating extra wiring work for yourself if the easiest route is effective. You can always go back and add more adhesive or screws later IF it becomes necessary.
The other option is actually a peel-and-stick wire – usually two leads – that resembles a flat plastic trim piece. This can be nice and unobtrusive, but I think it’s far less versatile. A wire channel lets you add additional wiring later, and allows for connections that require more than two leads.