RV Electrical Problems on the Road

You turn the key and get nothing. Or the engine fires right up but the inside of the coach is dark. Or the microwave works on shore power and dies the second you unplug. All three of those get called an electrical problem, and they are three completely different problems.

Ten minutes of understanding what is actually wired to what will save you a lot of guessing on the side of the road.

Your RV has two electrical systems

The first is 12-volt DC. Same idea as your car, and it runs off batteries. A motorhome usually has two separate battery banks: the chassis battery, which starts the engine and runs the dash, and the house bank, which runs everything in the living space. Lights, water pump, furnace fan, fridge controls, slide motors, jacks, the propane detector. A travel trailer or fifth-wheel has no chassis battery. It has a house battery, and the tow vehicle feeds it a trickle down the umbilical cord while you drive.

The second system is 120-volt AC, which is regular household current. It comes from a campground pedestal through your shore cord, from your onboard generator, or from an inverter. It runs the air conditioning, the microwave, and the wall outlets.

Two more words worth knowing. A converter takes 120-volt shore or generator power and turns it into 12-volt to run the house circuits and charge the house batteries. An inverter does the reverse, turning battery power into household current so an outlet works with no shore power. Many rigs have one box that does both.

Once you know which system a dead thing lives on, you have already cut the problem in half.

Nothing works at all: start at the batteries

If the whole rig is dead, do not go looking for exotic causes. Start where the power comes from.

• Check the battery disconnect switch, usually inside a bay door or near the entry step. It gets bumped, or somebody flipped it at the end of last season and nobody remembers.
• Look at the terminals. Corroded or loose terminals are the single most common electrical fault on any RV. A connection that looks a little grungy can still be an open circuit under load.
• Check the water level if you have flooded lead-acid batteries. Plates exposed to air are already damaged.
• Check the main fuse. There is usually a large inline fuse or breaker between the battery bank and the distribution panel. If it popped, everything downstream is dead.
• Measure voltage if you own a meter. A resting 12-volt lead-acid battery reads around 12.6 volts. At 12.0 it is about half dead. Under 11.8 it will not run much of anything.

The house is dead but the engine cranks fine

That tells you the chassis side is healthy and the house side is not, which is good news, because you can still drive.

Likely causes in order: the disconnect is off, the house bank is discharged, a main fuse to the house panel is blown, or the converter quit charging and the bank has been slowly draining for weeks without you knowing.

The reverse case, where coach lights work but the engine will not crank, usually means a dead chassis battery or a failed battery isolator. That isolator lets the alternator charge both banks while you drive but keeps house loads from draining your starting battery when parked. When it fails, one bank stops getting charged and nobody notices until it is flat.

The 120-volt side: shore power, generator, converter

If your outlets and air conditioning are dead but your lights and water pump still work, the 12-volt system is fine and the problem is on the household side.

1. 1Reset the GFCI outlet. Every RV has at least one, usually in the bathroom or the galley, and it protects a whole chain of other outlets. A tripped GFCI in the bathroom kills the outlet behind the TV, and nobody thinks to look.
2. 2Check the breakers in the 120-volt panel. Look for one sitting slightly out of line with the others. Push it fully off, then back on.
3. 3Check the shore cord and the pedestal. Burned or melted prongs on a 30-amp or 50-amp plug are extremely common and are a genuine fire hazard. So is a bad campground pedestal.
4. 4If you are on the generator, check the generator's own breaker. Generators have breakers separate from the coach panel.
5. 5Check the transfer switch if the generator runs fine but nothing inside gets power. That is the box that decides whether the coach is fed by shore power or generator, and its contacts burn up over time.

Trailer owners: check the seven-way plug first

If you are towing and your trailer brakes, running lights, or turn signals quit, the seven-way connector between truck and trailer is the culprit far more often than anything else. It lives at bumper height and gets rained on, salted, dragged, and packed with road grime.

Pull it apart and look. Green corrosion on the pins, a bent pin, a spread contact that no longer grips. Clean it with a small wire brush or contact cleaner and pack it with dielectric grease. Then check the ground. A huge share of weird trailer gremlins, lights that dim when you brake, brakes that cut in and out, turn signals that make the running lights flicker, are nothing but a bad ground.

What is safe to check on the shoulder, and what is not

Fuses, breakers, GFCI resets, battery terminals, disconnect switches, the seven-way plug. All fair game. Bring a flashlight and take your time.

What you should not do: work on anything 120-volt with the shore cord plugged in or the generator running. Do not lay a wrench across battery terminals, because a shorted battery can throw molten metal. And do not bypass a fuse with a bolt. A fuse that keeps blowing is telling you something, and jumping it just moves the failure into the wiring, which then becomes a fire.

If you smell hot plastic or see a wire or connector that has discolored or melted, shut the system down and stop right there. An RV fire goes from a faint smell to unsurvivable in a couple of minutes.

Electrical faults are miserable to chase with a flashlight in a parking lot and pretty quick with a meter and some experience. Duckett Roadside Repair works on RV and truck electrical systems where you sit, from Milton and Pace out to Navarre, Gulf Breeze, Crestview and the I-10 corridor. Call (850) 495-0366 any hour, any day, and be ready to say exactly which things work and which do not. That is the fastest way to get the right parts on the truck the first time.