RV Electrical Problems: A Shop's Order of Operations
· 5 min read
The short version
Start every RV electrical problem by asking whether the dead component runs on 12 volt DC or 120 volt AC, because those are two nearly separate systems and the answer halves your search.
From there, test in order: pedestal, cord and inlet, transfer switch, breaker panel, converter output, fuse block, and grounds. Stop at the transfer switch, the inverter DC bus, or any smell of hot plastic.
You reach up to switch on the bedroom light and nothing happens. Then you notice the microwave clock is still lit, so the coach clearly has power. Or the opposite happens: every outlet in the rig is dead, but the ceiling lights are fine and the water pump still runs. Owners often start pulling fuses at random at this point, or worse, start swapping parts. Ten minutes of thinking saves an afternoon of that. The first question is not what broke. The first question is which of the two completely separate electrical systems in your RV the dead thing belongs to.
Your RV runs two power systems that share a coach and almost nothing else. One is 12 volt DC, fed by your house batteries and topped up by the converter, the alternator, or solar. It runs lights, the water pump, furnace and refrigerator control boards, slide and leveling motors, and vent fans. The other is 120 volt AC, fed by shore power, the generator, or an inverter. It runs outlets, the microwave, the roof air compressor, and the electric element in the water heater. Knowing which side is dark cuts your search space roughly in half before you touch a single tool, and it is the first thing we sort out on any [RV electrical repair](/services-brea/rv-electrical-repair-brea) that comes through the door.
Is the dead thing on 12 volt DC or 120 volt AC?
Start by cataloguing what still works, not what does not. If the ceiling lights, the water pump, and the refrigerator control panel are all alive, your DC side is healthy and you have a 120 volt problem. If the outlets and microwave work but half the lights are out, it is the reverse. If everything went dark at once, you are looking at something upstream of both, usually the pedestal, the cord end, or the transfer switch. Write the working and non-working list down before you open anything. That list is most of the diagnosis, and it takes two minutes.
| What is dead | 12V DC or 120V AC | What the pattern usually points to |
|---|---|---|
| Ceiling lights, water pump, furnace fan, slide motor | 12V DC | Battery disconnect, main DC fuse, or a converter that stopped charging |
| Wall outlets, microwave, roof air compressor | 120V AC | Pedestal, cord end, transfer switch, or a tripped branch breaker |
| Refrigerator runs on gas but the control panel is dark | 12V DC | Fuse block or a poor ground at the refrigerator chassis |
| Refrigerator cools on gas but not on electric | 120V AC | Heating element or the branch circuit feeding it |
| Everything at once, no lights and no outlets | Both | Pedestal breaker, cord end, or a failed transfer switch |
| Lights dim noticeably when the pump runs | 12V DC | Voltage drop from a weak battery or a corroded ground |
| Some outlets dead, others live | 120V AC | A tripped GFCI upstream, often in the wet bay or an outside compartment |
How do you tell which leg of the power triangle failed?
Shore power, converter, and battery form a triangle, and each leg fails differently. With the coach plugged in and the batteries disconnected, if the 12 volt lights still work, your converter is producing. Plug in with the batteries connected and measure right at the battery terminals: a healthy converter holds around 13.6 volts, and anything sitting at 12.4 volts with shore power connected means the converter is not charging. Unplug, wait, and a good battery bank should hold above 12.4 volts at rest. Three quick checks and you know which leg is down.
A dead battery bank can also fake an AC problem. Some transfer switches and inverter chargers need house DC voltage to hold their relays closed. Drop below roughly 10.5 volts and they release, and suddenly your outlets go dark even though the pedestal is perfectly fine. We get that call every summer. The owner has already replaced a cord and a breaker before anyone thought to measure the battery.
What order should you actually test in?
Testing in order matters because each step is a gate, not just a data point. A good reading tells you the fault lives further downstream, and a bad one tells you to stop right there and look closer. Skipping ahead is how people end up condemning a converter that was never the problem, or replacing a cord because the panel looked fine. Work with the coach plugged in, keep one hand in your pocket, and treat every AC connection as live until your meter says otherwise.
The sequence we use on the shop floor:
- Pedestal: check for 108 to 130 volts between hot and neutral, correct polarity, and a real ground. Use a plug-in tester first, then the meter.
- Cord and inlet: confirm the same voltage at the coach inlet, then inspect the blade ends for heat discoloration or pitting.
- Transfer switch or inverter pass-through: confirm voltage going in and voltage coming out. This is the most common silent failure on a coach with a generator.
- Main breaker panel: check voltage at the main lugs, then at each branch breaker, including the ones that look fine.
- Converter output: measure DC right at the converter terminals, not at a distant fuse block.
- 12 volt fuse block: check both sides of every fuse with the circuit live, rather than eyeballing the element.
- Grounds: the chassis stud, the battery negative, and the ground at any component behaving strangely.
What does a multimeter really tell you?
A meter reading a circuit with no load on it tells you almost nothing. A 12.6 volt resting reading at a battery means the surface charge is fine and nothing else. Turn on the water pump and the furnace fan, watch the same terminals, and if the number falls under 11.8 volts you have found a battery or a connection that cannot carry current. That drop under load is the whole test. Resting voltage is a snapshot of a battery doing no work at all.
The same idea applies to connections. Continuity mode tells you two points are joined. It does not tell you the joint is any good. Instead, put the meter across the connection itself while the circuit is running and read the voltage drop. More than a couple of tenths of a volt across a single crimp, terminal, or ground lug means resistance is turning your power into heat right at that spot. That is how you catch a bad connection that passes a continuity test all day long.
What goes wrong at the pedestal before you ever plug in?
Two faults show up constantly at parks: reverse polarity and an open ground. Reverse polarity means hot and neutral are swapped somewhere in the pedestal wiring, so your appliances still run but the switched side of every circuit stays energized when it should be dead. An open ground means the safety return path is missing, so a fault that should trip a breaker instead sits on the coach skin waiting for you. An inexpensive plug-in tester catches both in three seconds. Do not skip it because the pedestal looks new. We have seen brand new pedestals miswired straight from installation.
Why is a corroded chassis ground the most common intermittent?
If something works sometimes, suspect a ground before you suspect the device. Almost every 12 volt circuit in a coach returns through the frame, and those ground straps land on a painted or powder coated chassis stud that collects water, road grime, and vibration. Corrosion there adds resistance. Resistance shows up as a dim light, a slow slide motor, a step that stalls halfway out, or a control board that resets whenever the compressor kicks on. Pull the stud, wire brush both the lug and the frame down to bright metal, add a star washer, torque it, and coat it. That one repair closes more intermittent complaints than anything else we do.
When should you stop and hand the coach over?
Stop at four things. Anything inside the automatic transfer switch, because it is fed by two live sources and the interlock is what keeps them apart. Anything on the DC bus of an inverter, where a 400 amp battery cable can vaporize a wrench. Anything involving lithium battery management, since a BMS that has locked out is protecting the pack for a reason and forcing a charge into it is dangerous. And any smell of hot plastic anywhere in the coach, which means a connection has been running hot long enough to melt insulation. Kill the power at that point, both shore and battery, and get it looked at.
Frequently asked questions
How do I tell whether my RV converter or my battery is the problem?
Measure at the battery terminals with shore power connected. A working converter holds roughly 13.6 volts there. If you see 12.4 volts or less while plugged in, the converter is not charging. Then unplug and check resting voltage after an hour. A bank that cannot hold 12.4 volts at rest is the battery, not the converter.
Why do my RV ceiling lights dim when the water pump kicks on?
That is voltage drop under load, and it points at either a tired battery bank or a high resistance connection. Watch the battery terminals while the pump runs. If the terminals stay near 12.4 volts but the lights still dim, the loss is in the wiring or a ground. If the terminals themselves sag, the battery is the weak link.
Is it safe to camp on a pedestal that shows an open ground?
Treat it as not safe and report it to the park office. An open ground removes the fault path that trips a breaker, which means a short can energize the coach skin instead. Move to another site until it is corrected. Confirm any electrical code question with the park operator or your local building authority rather than assuming.
What should my house battery read while it is under load?
Load it with the water pump and the furnace fan together, then watch the terminals. A healthy flooded or AGM bank stays above about 12.0 volts through that. Falling under 11.8 volts within a minute means the bank has lost capacity or a cable connection is adding resistance. Retest after cleaning both battery terminals down to bright metal.
Can a failing transfer switch kill only part of my 120 volt system?
Yes, and it is a common pattern. Many transfer switches pass two legs, and one set of contacts can burn while the other keeps working. You end up with half the breaker panel live and half dead, which looks like a panel problem. Confirm by measuring voltage in and voltage out on both legs of the switch.
Written and reviewed by the OCRV Center Technical Team. Last updated .
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Referenced on this page
- RV electrical repairPanel, converter, transfer switch, and grounding work on coaches and trailers.
- Solar and battery systemsFor lithium conversions, BMS behavior, and charge source conflicts.
- Generator repairWhen the AC side only fails on generator power and not on shore power.
- Why a generator will not startThe other half of the AC power question, starting with fuel level.
- Slide out will not retractA slide that stalls is very often a 12 volt supply or ground problem.
- Our repair processHow we scope an electrical diagnosis and document what we find.
- Contact the shopIn shop diagnosis only. We do not run mobile or roadside service.