Inspecting RV Electrical: 12V, 120V, Converter, Inverter, Solar

An RV runs two separate electrical systems at once: a 12-volt DC side that powers your lights, water pump, fans, slide-outs, and control boards, and a 120-volt AC side that powers your outlets, microwave, and air conditioner when you plug into shore power or a generator. Test both, confirm the converter charges the battery and the inverter (if present) actually runs outlets off the battery, and treat dim lights, a dead battery, or a burnt smell as reasons to slow down, not push through. Most electrical faults are cheap, but a few (corroded wiring, a fried converter, a melted shore cord plug) hint at deeper neglect.

Electrical is the one system where a nervous buyer can do real damage to a seller's "it all works" story in about twenty minutes, with no tools beyond a phone, a plug-in outlet tester, and patience. You are not trying to become an RV electrician. You are trying to confirm power flows where it should and to catch the handful of expensive or dangerous problems before you wire money. When you are ready to sanity-check a specific unit, you can get your RV verdict on the listing before you ever drive out to see it.

The Two Systems, In Plain English

Every modern RV (whether it is a travel trailer, a fifth wheel, or a Class C motorhome) carries two parallel electrical systems. Understanding the split is half the inspection.

12V DC (the house battery side). This runs off the deep-cycle house battery (or batteries). It powers interior LED lights, the water pump, the furnace fan and ignition, range hood, the bathroom fan, slide-out and stabilizer motors, the propane/CO detectors, and the brains of the fridge and water heater. If the 12V side is dead, almost nothing works even when you are plugged in, because most "appliances" need 12V logic to turn on. This is the system new buyers most often misunderstand.

120V AC (the shore power side). This is regular household-style power. It feeds the wall outlets, the microwave, the rooftop air conditioner, the TV, and the converter. It comes from one of three places: a shore power pedestal at a campground (30-amp or 50-amp), a portable generator, or in a motorhome, the onboard generator. No shore power and no generator means no AC outlets, no microwave, no air conditioning.

The converter is the bridge. When you are plugged into 120V shore power, the converter takes that AC and turns it into 12V DC to run the house and charge the battery. If the converter is dead, the battery slowly drains even while you are plugged in, and you will be confused about why your lights die overnight at a full-hookup site.

The inverter is the reverse bridge (and is optional). It takes 12V battery power and turns it into 120V AC so you can run outlets without shore power. Many basic trailers do not have one. If the seller claims "you can boondock and run the TV," there must be an inverter, and you should make it prove itself.

Before You Touch Anything: The Cold Walkthrough

Do this first, before the seller plugs anything in, so you can see the system "cold" and "hot."

• Open the battery compartment. Look at the battery type, the date, and the terminals. A flooded lead-acid battery typically lasts 3 to 5 years; an AGM 4 to 7; lithium (LiFePO4) often 8 to 10+. Check for a date sticker or manufacture code. White or blue-green crust on the terminals is corrosion, usually a cheap clean-up but a sign of casual maintenance.
• Find the converter and breaker panel. It is usually a metal box near the floor, often behind a panel, with a row of household-style breakers above a row of automotive blade fuses. Sniff it. A burnt, fishy, or melted-plastic smell is a real warning.
• Inspect the shore power cord and plug. Pull it out fully. Look at the prongs on the male end. Browned, pitted, or melted prongs mean the RV has been pulling more current than the connection could handle, often from a loose pedestal or an overloaded circuit. A new cord is $80 to $200; a melted inlet on the RV is a bigger and pricier fix.
• Count the batteries and note the wiring. Two 6V batteries wired in series, or two 12V in parallel, is common and fine. Mismatched batteries (different brands, ages, or one swollen) signal a patch job.

A swollen, bulging, or leaking battery is a walk-away-or-renegotiate item, not because the battery is expensive, but because it tells you nobody was watching.

The Hot Test: Powering It Up

Now ask the seller to connect to shore power (a standard 15A house outlet with the right adapter is fine for testing most things except the air conditioner). Better yet, test at a site with a real 30A or 50A pedestal. Work this checklist in order.

Carry your own outlet tester and a phone flashlight. The outlet tester alone will catch wiring mistakes that the seller genuinely does not know about, and it makes you look like you know what you are doing, which changes the negotiation.

Reading The Battery And Converter Honestly

The most common buyer trap is a dead or weak house battery masking everything else. If the battery is shot, you cannot fully test the 12V side, and a dishonest seller can hide a bad converter behind "oh the battery's just old."

Here is how to separate the two. With the RV unplugged, a healthy resting 12V battery reads about 12.6 to 12.7V. At 12.0V it is roughly half empty; at 11.8V or below it is nearly dead. Now plug into shore power and watch the same reading. Within a few minutes the voltage should climb above 13V as the converter pushes a charge. If it climbs, the converter works. If it sits at 12.2V while plugged in, the converter is likely dead or the battery won't accept a charge.

Rough cost ranges to keep in your head (always verify on the specific unit):

• Single 12V flooded house battery: $100 to $200
• Pair of 6V golf-cart batteries: $200 to $400
• Single 100Ah lithium (LiFePO4): $300 to $700
• Replacement converter (55 to 80 amp): $150 to $350 in parts, plus an hour or two of labor
• A modern converter/inverter combo or lithium-ready charger: $400 to $1,200

None of these are deal-killers on their own. What matters is whether the seller disclosed them and whether the price already assumes a fresh battery. If you suspect deeper trouble, our RV electrical problems guide breaks down the failure patterns, and the red flags checklist covers the seller behaviors that should make you cautious.

The Inverter And Solar Question

A growing share of used RVs are sold with "solar" and an inverter, and the words get stretched. Pin down exactly what is installed.

Solar comes in two very different forms. A "solar prep" or a single 100W panel that trickle-charges the battery is nearly worthless for running appliances; it just slows the battery drain. A real solar setup is 200W to 600W+ of panels feeding a proper charge controller (MPPT is better than PWM) into a meaningful battery bank. Ask to see the charge controller display in daylight. It should show watts coming in. No watts on a sunny day means the panels, wiring, or controller are not doing their job.

Make the inverter prove itself. Unplug shore power, switch the inverter on, and plug a small load (a phone charger or a lamp) into the outlets it feeds. Note that many installs only wire the inverter to one or two specific outlets, not all of them. If the seller says solar runs the air conditioner, be skeptical: running a rooftop AC off battery and inverter requires a large lithium bank and a 2,000W+ inverter, which is a serious and expensive build. Most "solar RVs" cannot do it.

Honest cost framing if you need to add or repair this yourself:

• 200W to 400W rooftop solar with MPPT controller, installed: $800 to $2,500
• 1,000W to 2,000W pure sine inverter: $200 to $700 in parts
• A full lithium plus solar plus inverter "boondocking" build: $3,000 to $8,000+

If solar and an inverter are a big part of why a unit is priced high, confirm they work on the spot. Paying a premium for a system you cannot verify is how buyers overpay.

Motorhome-Specific And Generator Checks

If you are looking at a Class A or Class B camper van, there are extra electrical layers, because the chassis (engine) battery, the house battery, and often an onboard generator all interact.

• Two battery banks. Motorhomes have a chassis/starting battery and separate house batteries. Confirm both are healthy and that a battery isolator or solenoid keeps them separate (so house use doesn't drain your starting battery).
• Onboard generator. Start it and let it run. Check the hour meter and compare it to the age of the rig. Very low hours on an old generator can mean it sat unused, which causes carburetor and seal problems; very high hours means heavy wear. See our generator hours guide for what's normal.
• Generator under load. Once it's running, fire up the air conditioner and microwave together. A healthy generator handles the load without bogging down or surging.
• Automatic transfer switch. In rigs with a generator, an automatic transfer switch (ATS) swaps between shore and generator power. A failing ATS can cause flaky power or a burnt-contact smell near the panel.

For van builds especially, electrical is often a custom job by a previous owner. Custom wiring can be excellent or terrifying. Ask who did it, ask for any documentation, and look closely for unfused connections, household (Romex) wire used where automotive wire belongs, and wire nuts rattling loose in a vibrating vehicle.

Questions To Ask The Seller

• "Is the house battery the original, and when was it last replaced?"
• "Has the converter ever been replaced or worked on?"
• "Does the inverter power all the outlets or just specific ones?"
• "Is the solar real panels with a controller, or just a solar-prep plug?"
• "Has the shore cord ever overheated or melted? Has the pedestal ever tripped?"
• "Has any wiring been modified or added by you or a previous owner?"
• "Can we plug in and run the air conditioner and microwave right now?"

Sellers who answer these calmly and specifically are usually telling the truth. Vague answers, "I never really used that," or refusal to plug in are themselves information.

When To Walk Away (Or Re-Price)

Most electrical issues are minor. These few are not, and they should either drop the price meaningfully or end the conversation:

• Burnt or melted smell at the converter, panel, or transfer switch. Heat damage means a fire risk and hidden wiring damage. Walk unless a professional inspects it first.
• Melted shore power cord prongs combined with scorching at the RV inlet. The cord is cheap; a damaged inlet and the wiring behind it are not.
• Breaker trips instantly every time you plug in. That's a short somewhere, and finding it can be slow and costly.
• Multiple outlets reading "open ground" or "reversed." Often DIY wiring done wrong, which raises questions about everything else that was "improved."
• A swollen or leaking battery plus signs nobody noticed. Pair this with water damage signs or a soft floor and you have a neglect pattern, not a one-off.

Electrical problems also rarely travel alone. A rig that was stored wet and ignored tends to have a tired battery, a corroded converter, and a roof you should also check. Run the unit through the full used RV inspection checklist and price the repairs into your offer with the offer calculator so you are negotiating from real numbers, not vibes.

FAQ

Can I test an RV's electrical from a regular house outlet? Mostly yes. A 15A house outlet with the correct adapter will power the converter, the 12V system, outlets, and the microwave. The one thing it usually won't run is the rooftop air conditioner, which needs a 30A or 50A pedestal or a generator. Test the AC separately if you can.

The lights are dim and the battery is dead. Is that a dealbreaker? Not by itself. A dead battery is a $100 to $400 fix. The real question is whether the converter charges a good battery. Plug in, watch the voltage climb above 13V, and you've confirmed the expensive part works. If it won't charge, factor in a converter too.

What's the difference between a converter and an inverter again? The converter turns shore power (120V AC) into 12V DC to run the house and charge the battery. The inverter does the opposite, turning battery power (12V DC) into 120V AC so you can run outlets without shore power. Every RV has a converter; not every RV has an inverter.

The seller says it has solar. How do I know if it's real? Look at the charge controller in daylight. A real system shows watts coming in from the panels and has a meaningful panel count (200W+) plus a proper controller. A single small "maintainer" panel or a bare "solar prep" plug is not a system you should pay extra for.

Is custom van or trailer wiring a red flag? Not automatically, but inspect it harder. Good custom work is fused, uses proper automotive wire, and is documented. Bad custom work uses household wire, wire nuts, and unfused runs. Ask who did it and look for melting, loose connections, and overloaded circuits.

Paste a listing and get your RV verdict before you drive out to see it.