Most RV electrical money is wasted by replacing parts in hope. The system is not complicated, it is a short chain of links, and a fault usually kills everything downstream of the link that failed. Learn the order and a symptom tells you where to look. This guide gives you the real layout, the actual voltage numbers a healthy system should show, and the measurement technique that finds the failed link instead of guessing at it.
Last reviewed: Sep 21, 2026, against current WFCO, Progressive Dynamics, Victron, Trojan, Lifeline and Renogy documentation. We update these guides when real-world data changes.
Look at the battery feed path: the disconnect, the main fuse, the battery terminals. If the converter is running, some 12 volt power should exist regardless of the battery.
The converter is carrying everything and the battery is not contributing. Either the battery is finished, or it is not being charged. Those are different problems with the same symptom, and the next section separates them.
The converter or its 120 volt feed. On shore power the converter should carry the whole load by itself, so the battery is not in the picture at all.
That branch fuse, or the load at the end of it. Nothing upstream is at fault, because upstream feeds the circuits that still work.
There is a short on that branch. Do not keep feeding it fuses. See the fused-circuit guide in this cluster, because tracing a short is its own skill.
Suspect the ground return. A bulb can have good power at the socket and still not light because the return path is corroded, which is why grounds deserve their own section below.
Parasitic draw. Something is drawing with the RV switched off, and the battery disconnect is the manufacturer's own answer.
Two things are worth understanding before you touch a meter, because both change how you search.
The battery feeds the panel, and the converter feeds the same panel. They meet at the DC bus rather than sitting in a line, and the converter's charging path runs backwards up the battery's own wire. WFCO states this in its own manual: a battery is not required for converter operation, and the battery works in conjunction with the converter to supply DC power. That single fact explains why an RV with a completely dead battery still has working lights when it is plugged in.
The frame of the RV is the negative conductor. Anywhere that return path is corroded, painted, or loose, current cannot get back to the battery and the device behaves as though it has no power at all. This is the single most misdiagnosed thing in RV electrics, because a bad ground presents as a fault in whatever device happens to be at the end of the circuit.
Start at the source and move outward. Battery voltage at the terminals, then at the disconnect, then at the main fuse, then at the bus, then at the branch fuse, then at the load. The first point where the reading stops being correct is where the fault is. Doing that in order is faster than testing anything at random, and it never leaves you replacing a part that was never broken.
Not every RV has a battery disconnect, and many towables use a resettable breaker near the battery instead of a switch. Motorhomes add a second battery for the chassis and a device that decides which battery gets charged, so a motorhome can show a charging fault that is really that device not closing, not the converter.
Progressive Dynamics states in its manual that the chassis bonding wire must be a separate wire run directly from the grounding lug on the converter, and warns against connecting the output negative to the chassis using the same wire. It is labelled a fire risk. Do not improvise that one.
This is the section that makes the rest of the guide useful, because it lets you check your own system against published figures rather than against a feeling. Battery numbers are chemistry specific, so find yours first.
These are Trojan's figures for a deep-cycle battery, and they are the classic shape: 100 percent reads 12.73 volts, 90 percent 12.62, 80 percent 12.50, 70 percent 12.37, 60 percent 12.24, 50 percent 12.10, 40 percent 11.96, 30 percent 11.81, 20 percent 11.66, and 10 percent 11.51. Charging set points from the same source are 14.7 volts absorption, 13.5 float, and 16.2 for equalization.
AGM. Lifeline publishes 14.3 volts plus or minus a tenth for absorption and 13.3 plus or minus a tenth for float, both at 77 degrees. Renogy's AGM manual sets a boost voltage of 14.4 and a float of 13.8, and states that the battery is considered fully charged when terminal voltage rises to 14.4 and fully discharged when it falls to 11.0. Note that AGM is not the same target as flooded, which is why a charger set for the wrong chemistry undercharges or cooks the bank over time.
A Renogy resting chart reads 100 percent at 13.6 volts, 90 at 13.4, 80 at 13.3, 70 at 13.2, 60 at 13.1, 50 at 13.0, 40 at 13.0, 30 at 12.9, 20 at 12.8, 10 at 12.0, and 0 at 10.0, with charging at 14.4 plus or minus a fifth. The caveat is theirs: the curve is much flatter for most of the usable range, so voltage alone tells you much less. Do not use a voltmeter as a fuel gauge on lithium. A shunt or a coulomb-counting monitor is the honest answer there.
Before you take any of those readings, Renogy states the battery must be disconnected from the system and allowed to rest for at least two hours. A reading taken while the charger is running, or minutes after you unplugged, is not a state of charge. This is why people conclude their battery is fine when it is not.
WFCO publishes an explicit pass test: if the voltage reads 13.6 volts DC plus or minus a fifth with no load, the converter is functioning properly. Some of their series state a wider window instead, 13.6 to 14.4 on the 8700-AD, and 13.6 to 14.6 on the lithium setting and the 8900-AD. On the lithium setting, or on an auto-detecting unit that has switched for lithium, the target is higher at 13.6 to 14.6. Progressive Dynamics publishes a nominal 13.6 volts, a boost mode around 14.4, and a storage mode around 13.2. Their operating modes are bulk at 14.4, absorption at 13.6, and float at 13.2.
A converter sitting at 13.2 volts is not necessarily broken, it may simply be in float because the battery is full. If you measure during float and conclude the converter is weak, you will replace a healthy unit. Force a load, like switching on lights or a fan, and watch whether it climbs into bulk.
The two-reading trick that solves most charging complaints. Measure at the converter, then measure at the battery, and compare. If the converter is producing 13.7 volts and everything between it and the battery is sound, you should see approximately the same figure at the battery. If you see 13.7 at the converter and only the battery's own resting 12.6 at the battery, the converter is fine and the fault is in the path between them: a breaker, a fuse, the disconnect, or a loose connection. The gap is the diagnosis.
This is the technique that separates a real diagnosis from a guess, and it is the thing almost no RV electrical page teaches.
Voltage drop only appears under load. Victron states it plainly: the drop becomes larger when the current increases. A circuit that reads perfectly with everything switched off can fail badly the moment it has to carry real current. This is exactly why a light tests fine at the socket and still will not light.
Put the circuit under its normal load, not idle. Measure the voltage at one end of the path, then at the other end, and subtract. Victron's own example is to load an inverter to maximum, measure across the DC connections at the inverter, measure across the battery terminals, and compare. The difference between the two readings is the voltage drop. The same method applies to any long run in the RV.
Victron advises aiming for no more than 2.5 percent, and publishes the equivalent for a 12 volt system as 0.3 volts. That is a useful hard number to carry in your head: if you are losing more than about a third of a volt along a path at full load, something in that path is resisting.
Victron lists the usual suspects: cable length and thickness, fuses, shunts, switches and breakers, loose connections, dirty or corroded contacts, and bad cable lug crimps. They also publish sample resistances, which is genuinely useful for calibrating your expectations. A single cable connection is about 0.06 milliohms. A 500 amp shunt is about 0.10. A 150 amp fuse is about 0.35. A two metre 35 square millimetre cable is about 1.08. Add enough of those and the total becomes visible as heat and as lost volts.
The trade method, and it is worth learning, is a comparison rather than a single reading. You measure the voltage across the battery, then measure the voltage across a loaded test bulb or device, and the two should be virtually identical. If they are not, there is a drop somewhere in the ground path. The important detail is the word loaded: use an old-fashioned incandescent test light that actually draws a few watts, because an ohmmeter uses so little current that it cannot tell you whether a ground connection will carry any real load. A ground can read perfectly on a meter and still fail the moment it has to work.
No RV manufacturer we looked at publishes a step by step, walk-the-chain voltage drop procedure for the 12 volt side. The method above is Victron's published technique, which comes from the power systems world, combined with the RV trade's two-reading approach. It is sound and it is used professionally, but we are not going to imply that a manufacturer wrote it for RVs specifically, because none did.
Owners lose real money to these four words, because they sound alike and do opposite things.
Takes 120 volt shore power and turns it into 12 volt DC. It runs your lights, fans, water pump and control boards.
Goes the other way. Takes 12 volts from the batteries and steps it up to 120 volts AC so household outlets work when you are not plugged in.
This is the honest name of the thing most RVs actually have, because it does both jobs: it runs the 12 volt system and it charges the battery. WFCO calls its unit a Converter-Charger and Progressive Dynamics calls theirs a Converter/Charger. If someone tells you to replace your converter when you have an inverter charger, you have been given the wrong advice, because there is no separate converter in that RV.
One unit doing both jobs with an automatic switchover, and it replaces the converter in many mid-range and higher end RVs. When one of these is fitted, the old converter is disconnected and becomes obsolete.
An isolator uses diodes that behave like one-way valves, and the honest cost is roughly 0.7 volts lost across them. An ACR combines the batteries while charging and separates them when charging stops, closing at around 13.0 volts and opening at around 12.75. A BIRD is the motorhome version that charges the coach battery from the alternator and the chassis battery from the converter, closing at about 13.3 volts and dropping out at about 12.8. That last part matters for diagnosis: if a BIRD is not closing, your chassis battery will not charge on shore power and it will look exactly like a failed converter.
Solar only. It regulates what the panels put into the battery and stops them overcharging. It is not part of the converter circuit at all, and a fault there will not affect shore power operation.
RV fuses are not mysterious once you know which is which.
Branch circuits use ordinary automotive blade fuses. WFCO specifies ATC or ATO types, naming Littelfuse type 257 and Bussmann type ATC as examples, so replace like for like rather than whatever fits the slot.
High-current feeds use bolt-on fuses. A fuse manufacturer's own guidance is that mid-range feeders take MIDI style, and main battery feeds, alternator lines and inverter inputs take ANL style in roughly the 35 to 400 amp range. High-draw loads like slide-outs and leveling jacks often use resettable breakers instead.
The main fuse, which protects the battery feed to the panel. Its rating is specific to your panel, so check rather than assume. WFCO publishes the battery circuit fuse per model, in one series it is a 30 amp fuse on a numbered circuit that differs by model.
These are on the converter itself, usually two of them, and their only job is to protect the converter if the battery is ever connected backwards. WFCO is blunt about the trigger: a reversed battery connection, even if only for a second, will cause these fuses to blow. That is a very common self-inflicted fault after battery replacement, and it presents as a converter with no DC output at all. Their published instruction is to check the reverse polarity fuses first, inspect for a break in the element, and if there is no visible break, check continuity. Ratings vary by model, in one series running from a single 40 amp fuse up to two 40s depending on output.
Inspect the fuse element visually, then confirm with continuity. For voltage, measure both sides of the fuse under load, because a good fuse reads the same on both sides and a failed one does not. For an AC breaker, a tripped one sits in the off or middle position, and the reset is to push it fully off and then back on, not just to flick it. An open circuit is what remains when the fuse is good, the voltage is absent, and the continuity test does not explain it, which is when you go looking upstream.
In an RV, the chassis is the negative conductor. It is not an earth ground in the household sense and does not need to be. It is simply the return path, and every device depends on it.
Every connection point between two different metals is a corrosion site once moisture is involved, and corrosion raises resistance until the connection effectively disappears. The result is a device that has proper voltage at it and still will not run, which sends people looking at the device instead of the frame.
If the bulb or device tests correctly with an ohmmeter, and correct voltage is present in the socket, and it still does not work, the return path is the suspect. That specific combination is the signature.
Use the loaded comparison described in the voltage-drop section. The reason an ohmmeter is not enough is worth understanding: it pushes so little current through the connection that it cannot tell you whether that connection will carry a real load. A ground bond can read a fraction of an ohm and still fail under ten amps. Loaded testing is the only honest test.
On the 120 volt side, shore power grounding is a genuinely different issue with a safety dimension, including what is often called a hot skin condition where touching the RV gives a shock. That is not the 12 volt ground return and should not be treated as the same fault. If you feel a tingle from the vehicle body, stop and treat it as an AC grounding and bonding fault, not a 12 volt one.
We could not find a manufacturer service manual that contains a dedicated 12 volt ground-return test procedure. This is trade knowledge rather than documented manufacturer procedure, and we would rather say that than imply otherwise.
There is no published acceptable total draw figure for an RV. Winnebago's own service document declines to give one, stating that you must understand the electrical equipment on your specific vehicle to know what is normal, and that typical owner manuals do not share that detail. They list the usual culprits: slide-out control modules, electric step modules, radio memory, engine and transmission computers on the chassis side, and TVs, inverter chargers, the LP gas shut-off solenoid and illuminated touch panels on the house side. Their recommended countermeasure is refreshingly simple: use the battery disconnects provided.
Individual components do publish their draws, which lets you add up your own RV. A BIRD control module is under 2 milliamps at standby. A Blue Sea ACR draws under 40 milliamps to monitor and about 13 while operating. A 1500 watt inverter can draw 500 to 600 milliamps at no load, and a 2000 watt inverter charger lists 25 watts idle in normal mode. Two or three of those together turn into a genuinely flat battery over a month.
Disconnect the negative battery cable, connect the meter between the battery post and the cable you just removed, so all current runs through the meter. Let the vehicle sit for ten to forty five minutes first, because modules need to go to sleep and an early reading includes things that will switch off. Then pull fuses one at a time and watch the current: when it drops significantly, you have found the circuit. If nothing much changes, use the battery disconnect and accept that this is what the disconnect is for.
What counts as normal, with the caveat attached. The figure most often quoted in the trade, and it comes from a meter manufacturer's general automotive guidance rather than from an RV source, is that below 50 milliamps after the vehicle is asleep is normal and above 100 milliamps is suspect. Treat it as a starting point, not a rule, because the manufacturer who would actually know has declined to publish one. You can also work it backwards: if you lost 48 amp hours over 12 days, that is 4 amp hours a day, which is 166 milliamps, and that is a real and findable draw.
We found pages claiming that 500 milliamps is healthy and that one to two amps is typical. Those figures are many times the meter manufacturer's guidance and appear to be generated rather than sourced. If a page tells you a one amp draw is normal, it is describing a battery that will be flat in a fortnight.
Worth separating, because a lot of confident advice online is field lore repeated until it sounds official.
Progressive Dynamics publishes a proper troubleshooting table, which is unusual and useful. On no output, their listed causes are that AC power is not connected, that external fuses are blown (typically through reverse polarity), a short circuit, a shutdown from overheating, or a shutdown from over voltage, which occurs above 132 volts input. On low output, they list an excessive load for the converter, an input voltage outside 105 to 130 volts, or a battery with a bad cell. WFCO adds that on a short circuit the converter will drop its output to zero, and that under excessive load the current holds constant while the voltage falls. WFCO also notes that if the converter reads zero at the battery, you should check for an open inline fuse in the battery wire circuit.
Cooling fan failure leading to a slow heat-related death is widely described in the trade and appears in no manufacturer document we could find. Pitted contacts in a battery disconnect, corroded terminals and ground points, and converters wearing out from heat, vibration, moisture and surges are all the same category. They are probably real, and they are not manufacturer-documented causes, so treat them as strong suspicion rather than specification.
NFPA 1192 points to a separate standard for low voltage systems in RVs, and that standard is sold for around 45 dollars with no free copy available. The marine equivalent, which the RV world borrows much of its practice from, is similarly paid. That means some of the most authoritative rules about RV wiring are not publicly readable, including the wire-sizing tables and the requirement that a main fuse sits close to the battery. We are not going to paraphrase rules we could not actually read.
No manufacturer publishes repair pricing, so every figure below comes from service companies and is a range rather than a quote.
A diagnosis runs roughly $150 to $285, and some shops credit it against the repair. A mobile technician call including a minor fix such as a loose connection, a bad fuse or a dead outlet is around $150 to $400. Given how often the answer turns out to be a fuse or a connection, paying for the diagnosis is usually the cheapest path to being right.
Converter replacement is broadly $400 to $1,200 installed, with one service source quoting $500 to $520 installed for a common 55 to 60 amp unit in a specific brand of trailer. Repairs rather than replacement are quoted anywhere from $150 to $900.
Large inverter chargers are a different grade and are quoted from $750 up to $4,500, with labor described as three to fourteen hours at shop rates that can exceed $250 an hour.
Distribution panels are surprisingly cheap as parts: a bare AC panel is around $75 to $110, an AC and DC panel around $100, and a full replacement power centre section closer to $427. The labor is the cost here, not the part.
A disconnect switch is about $40 for a simple manual on-off switch, while a motorhome battery control panel runs roughly $157 to $245.
If a shop quotes a converter replacement, ask whether the reverse polarity fuses were checked first and whether the fault was confirmed by measuring at both the converter and the battery. Those two questions cost nothing and they eliminate the most common false diagnosis in this system.
This page is the hub. When you know which link has failed, one of these goes deeper on that specific fault.
Fuse keeps blowing. Tracing an actual short, which is its own skill and not the same as replacing a fuse. Four documented methods, including the test light trick that lets you hunt the fault live without blowing anything.
Converter not charging the battery. The specific case where the converter tests fine and the battery still will not charge. Includes the maker's pass test and the two-reading method that proves which side is at fault.
Generator not charging the house batteries. The same symptom arriving from a completely different source, because a generator never charges the battery directly.
Lights not working. One fixture, one circuit or all of them each points somewhere different. Covers why a light can show full voltage at the socket and still be dead.
Outlets not working. The 120 volt side rather than 12 volt, including the three published reasons a GFCI will refuse to reset.
Solar not charging. Panel, controller, battery, and the two things that look like faults and are not.
If your symptom is specifically weak or lost 12 volt supply in cold weather, the low voltage section of our furnace troubleshooting guide covers how a sagging battery stops an appliance that needs current to start. And battery winter storage covers what happens to a bank that sits, which is where a lot of these faults begin.
Test whether it happens when you are unplugged. If the lights are dim only when you are running on battery, the fault is on the battery side, either capacity or charging. If they are dim while you are plugged into shore power, the fault is the converter or its 120 volt feed, because on shore power the converter should be carrying the whole load and the battery is not involved. That single question splits the system in half.
That gap is the whole diagnosis. The converter is producing correctly, so the fault is in the path between the converter and the battery, not in the converter. Working that path you find the reverse polarity fuses, the main battery fuse, the battery disconnect switch, and loose or corroded connections. Measuring at both ends and comparing is faster than checking any of those one at a time.
A converter takes 120 volt AC shore power and turns it into 12 volt DC, which is what runs your lights, fans, water pump and control boards. An inverter goes the other way, taking 12 volt DC from the batteries and stepping it up to 120 volt AC so you can run household outlets when you are not plugged in. Many RVs now have an inverter charger, which is one unit doing both jobs, and in those the converter is usually gone.
Voltage drop only appears under load, so a reading taken with everything switched off tells you almost nothing. Load the circuit, then measure the voltage at both ends of the same path, for example at the battery terminals and again at the device. The difference between the two readings is the voltage drop. Manufacturer guidance suggests aiming for no more than 2.5 percent, which on a 12 volt system is about 0.3 volts.
Because things are not actually off. Control modules for slide-outs and steps, radio memory, the LP gas solenoid, and illuminated touch panels all draw current continuously. The practical answer is the battery disconnect, which is what the manufacturer recommends. To measure it, put a meter in series with the negative cable at the battery and pull fuses one at a time until the current drops.
No manufacturer publishes a figure for a whole RV, and at least one major manufacturer states outright that it depends on the specific vehicle and declines to give a number. A meter maker's general automotive guidance is that under 50 milliamps after the vehicle has gone to sleep is normal and over 100 milliamps is suspect. Individual components do publish their own standby draws, so you can total those for your own RV.
The manufacturer and agency documents this guide draws on, so you can check any figure for yourself.