On this page (6 sections)
Two systems, one vehicle
The 120-volt side is what arrives from a pedestal or a generator: shore cord, transfer switch, main distribution panel, breakers, and the outlets, air conditioners, and appliances beyond them. The 12-volt side runs the pumps, lights, fans, slide and jack motors, control boards, and the ignition circuits on gas appliances. They meet at two devices. A converter takes 120 volts in and charges the batteries. An inverter takes battery power and makes 120 volts when nothing else is available.
That intersection is where confusing symptoms come from. A refrigerator that will not light on propane because a 12-volt control board is starving, an air conditioner that will not start because pedestal voltage is sagging under load, lights that dim when the water pump runs because of a bad ground rather than a weak battery. Working one system in isolation while ignoring the other is why these faults get chased for months.
Chassis systems are a third domain again on motorized units, with a starting battery, an alternator, and a charge relay tying the two battery banks. When that relay sticks closed, the house loads drain the starting battery. When it fails open, the alternator never charges the house bank while driving. Neither shows a fault code, and both present to the owner as batteries that will not hold a charge.
What actually goes wrong
Connections, overwhelmingly. Recreational vehicles vibrate constantly, they are assembled quickly, and they use crimped terminals in places exposed to moisture. A crimp that has corroded internally still looks perfect from the outside and still passes a continuity check with no load on it, then drops significant voltage the moment current flows. Voltage drop testing under load is how those are found, and it is why a meter reading of twelve point six volts at rest proves very little.
Ground paths cause the second tier of complaints. On a vehicle where the frame, the aluminum cage, and the appliance chassis all serve as return paths in different places, a single corroded ground stud produces symptoms in devices that share it and nowhere else. That is why a fault can look like it is in the water pump, the lights, and the control board simultaneously, and why replacing all three changes nothing.
Shore power faults are their own category. Reverse polarity and open ground at a campground pedestal are common and can damage equipment. A 50-amp service is split phase, two 120-volt legs, and losing one leg leaves half the coach working normally while the other half is dead, which owners reasonably interpret as a breaker problem inside. Transfer switches also fail with contacts welded or burned, usually announcing themselves with heat damage inside the housing.
How the diagnosis is run
Diagnostics are billed at $285 per hour with a one hour minimum, credited against an authorized repair, and the method is deliberately unglamorous. We reproduce the fault, then measure at the source, at the distribution point, and at the load, under actual operating current. That sequence isolates whether the problem is supply, distribution, or the device itself, which is the question that has to be answered before anything is ordered.
On the 12-volt side that means load testing batteries rather than reading resting voltage, checking for parasitic draw with a clamp on the negative leg, verifying converter output under charge, and performing voltage drop tests across suspect runs and grounds. On the 120-volt side it means checking incoming pedestal quality, verifying transfer switch operation on both sources, and confirming that each leg of a split phase service is present and balanced.
Thermal inspection catches what meters miss. A connection that is developing resistance generates heat before it fails outright, so a scan of the distribution panel, the transfer switch, and the main lugs under load frequently identifies the next failure before it happens. On coaches that have had aftermarket equipment added by several different installers over the years, that scan is regularly the most valuable ten minutes of the job.
Upgrades, conversions, and what we do not do
Lithium iron phosphate conversions are the most requested upgrade, and they are not a drop-in swap on most units. The existing converter charge profile is built for lead acid and will not fully charge or properly manage a lithium bank. Alternator charging needs a DC to DC unit to avoid overloading a stock alternator. Cable sizing that was adequate for a modest lead acid bank is often inadequate for the current a lithium system will happily deliver into a fault.
Solar and inverter installations are the other common project, and the details that matter are the ones nobody photographs: correct controller type and sizing for the array, proper fusing at every source of current, cable runs sized for the actual distance rather than the nearest convenient gauge, and mounting that does not create six new roof penetrations without proper sealing. We handle the roof side of that work as carefully as the electrical side.
On commercial vehicles our electrical scope is deliberately bounded. Body electrical, lighting, upfit and equipment installation, and the wiring associated with structural and body repair are all in scope. Engine management, drivetrain electronics, and inspection services are not work this shop performs, and we say so up front rather than partially disassembling a truck before discovering the limit. Everything happens in the building as well, since there is no mobile or on-site fleet service here.
What is included
- Fault reproduction under real load
- The condition is recreated and measured with current flowing rather than diagnosed from resting voltage.
- Voltage drop and ground path testing
- Suspect runs, crimps, and ground studs measured under load to find corrosion that looks fine externally.
- Battery, converter, and inverter testing
- Banks load tested, charge output verified, and inverter transfer behavior confirmed on both sources.
- Shore power and transfer switch inspection
- Pedestal quality, split phase leg balance, polarity, and switch contact condition checked and documented.
- Thermal scan of distribution points
- Panel, lugs, and transfer switch imaged under load to catch developing resistance before it fails.
- System upgrades installed to specification
- Lithium conversions, DC to DC charging, solar, and inverter work with correct fusing, cable sizing, and sealed mounting.
Signs you need this work
- Interior lights that dim noticeably when the water pump or a fan starts
- Half the coach dead on shore power while the other half works normally
- Batteries that read fine in the morning and cannot run anything by evening
- A converter or inverter that runs hot, buzzes, or trips its own protection
- A burning or hot plastic smell near the distribution panel or the transfer switch
- An air conditioner that will not start on one pedestal but starts fine on another
Frequently Asked Questions
My batteries read 12.6 volts but nothing works properly. Why?
Resting voltage tells you almost nothing about a battery under load. A bank with failed cells or heavy sulfation can show a healthy resting number and collapse the moment current is drawn. The same applies to connections: a corroded crimp passes a continuity check and drops significant voltage once current flows. We load test the bank and perform voltage drop tests across the runs and grounds, which is where these faults actually live.
Why does only half my coach have power at some campgrounds?
A 50-amp service is split phase, meaning two separate 120-volt legs feeding different halves of the distribution panel. If one leg is lost at the pedestal, in the cord, or at the transfer switch, everything on that leg goes dead while the other half operates normally. It reads like an internal breaker problem and usually is not. We test both legs at the inlet and through the transfer switch to find where the leg is being lost.
Can I just drop lithium batteries in place of my lead acid bank?
Rarely without other changes. The converter charge profile is designed for lead acid chemistry and will not correctly charge or manage a lithium bank. Alternator charging typically needs a DC to DC unit so a stock alternator is not overloaded. Existing cable and fusing sized for the old bank is often inadequate for the fault current a lithium system can deliver. We scope the whole system rather than only the batteries.
What does the diagnostic hour actually get me?
A measured answer rather than a parts sequence. Diagnostics are posted at $285 per hour with a one hour minimum, and that minimum is credited against an authorized repair. Within it we reproduce the fault, measure at supply, distribution, and load under real current, and thermally scan the distribution points. You get an explanation of what failed and why, whether or not you proceed with the repair here.
Do you install solar and inverter systems?
Yes, and the parts that determine whether it lasts are the unglamorous ones: controller type matched to the array, fusing at every current source, cable sized for the actual run length, and roof mounting that is properly bedded and sealed rather than screwed down and caulked. Because roof and structural work is done in this building, the mounting side is handled with the same care as the wiring.
Do you work on commercial truck electrical systems?
Within a defined scope. Body electrical, lighting, upfit and equipment installation, and the wiring tied to structural and body repair are all work we perform. Engine management, drivetrain electronics, and inspection services are not. We state that boundary before a vehicle is scheduled so nothing is discovered halfway through a job, and all of it is performed in shop rather than at your yard.
Related services
- Solar and Battery Systems
Lithium conversions, MPPT solar, inverters, and house bank builds.
- Generator Service and Repair
Onboard generator diagnosis, overhaul, and replacement.
- Slide Out Repair
Mechanism service, seal replacement, and slide room structural rebuild.