Motorhome and caravan electrics explained

Caravans offer a level of liberty and convenience to holidaymakers that’s rarely matched — when everything is going well, that is.

But what happens when things stop working? Scrambling around in the dark after a sudden loss of power is the last thing you want from your time off, especially if you have no idea what caused the problem or how to fix it.

Thankfully, you can future-proof your holidays from electrical failures by getting acquainted with how your caravan electrics work. Below, we’ve put together a guide that will teach you how your caravan electrical systems work — from wiring to power supplies — and how to troubleshoot properly when there’s a problem.

Caravan power supplies

The majority of caravan power comes from the mains. When you rent a caravan pitch at a campsite, you’ll almost always be given access to a mains electricity supply to keep everything running smoothly on your holiday.

But caravans actually have another energy supply: a built-in power source called a ‘leisure battery’.

What is a leisure battery?

A leisure battery is a power cell that provides back-up power when your caravan isn’t connected to the mains.

Whereas mains power can provide 240 Volts to appliances like fridges, hairdryers and heating, leisure batteries can only power 12 Volt appliances — typically, this will be low-voltage lighting and 12 Volt TVs. This means that many caravan electrical items won’t work when running on the leisure battery. Instead, it’s usually used to tide you over until you reach a campsite with a mains supply

How to charge a caravan leisure battery

The leisure battery is charged when you plug your caravan into the mains. It can also be charged by solar panels or generators, but you’ll usually have to install and connect these yourself.

Motorhome power supplies

Motorhomes are a little different from caravans in that they have two batteries — one for driving (vehicle battery) and another for everything else (leisure battery)

Vehicle battery

Just like a car or a van, motorhomes feature a vehicle battery in order to get you on the road. They’re used to start up the engine, as well as power things like headlights, taillights and indicators.

Vehicle batteries are charged when the engine is turned on. They can also be charged by an external source like the mains (when this powers both the vehicle and leisure batteries, it’s known as a ‘split charge relay’).

According to the AA, a staggering 25% of call-outs for motorhomes are related to battery failure. Because the vehicle battery feeds into the leisure battery, you can drain both by overusing the leisure battery.

Leisure battery

As in a touring caravan, the leisure battery in a motorhome is a separate 12V system from the vehicle battery. It kicks in when the vehicle is unplugged and the engine is not running. There might be more than one leisure battery depending on the model of motorhome you own.

Leisure batteries in motorhomes can be charged by the engine as well as by other power supplies like mains electricity, solar panels and generators.

Caravan towbar electrics

Caravans can be connected to your car so that you can control turn signals and tail lights while towing. They’re connected using a ‘trailer plug’ (also known as a caravan plug).

There are two types of trailer plug available to caravans: 7-pin plugs and 13-pin plugs.

7-pin (or “12 N-type”) trailer plugs

7-pin (also referred to as 12 N-type plugs) are commonplace among older caravans and offer a moderate level of functionality for caravans while being towed.

Below is a diagram of how a 12 Volt 7-pin trailer connector works:

1Red+12V for control valves
2BlackIgnition lock for electronics
3YellowGround for electronics
4BrownGround for control valves
5WhiteFault indication (when voltage is too low)
6Green/WhiteControl Active Network (CAN) Bus H (for brakes)
7Brown/WhiteCAN Bus L (for brakes)

13-pin trailer plugs

While a 7-pin plug only supplies things like basic lighting (like indicators and brake lights), 13-pin plugs boast a greater level of functionality. The additional pins in a 13-pin plug supply power for things like reversing lights and rear mist lights.

1YellowLeft turn signal
2BlueRear fog lamps
3WhiteGround for pins 1-8
4GreenRight turn signal
5BrownTail lamps and registration plate light
6RedStop lamps
7BlackTail lamps and registration plate light
8PinkReversing lights
9Orange+12V permanent
10Grey+12V via ignition lock
11Black/WhiteGround for pin 10
12Light grey(Reserved for future uses)
13Red/WhiteGround for pin 9

Troubleshooting issues with caravan electrics

If you’ve had plenty of use out of your caravan — or you purchased an older second-hand model — you may encounter the occasional issue with your caravans electrics.

Whether it’s the lights that aren’t working or a socket that won’t produce power, there are some troubleshooting steps you can take to figure out what the issue is and resolve it.

1. Problems with the leisure battery

If you’re not getting any power to your caravan or motorhome when relying on the leisure battery — even after you’ve been charging it for a substantial amount of time — then there could be a fault causing it to drain.

Here’s how you can determine the cause of the issue:

  1. Check the battery connections — All the cables should look clean with tight-fitting connectors; they shouldn’t come away with a light tug. Check for loose fittings and signs of corrosion around the battery terminals.

  1. Take a reading of the voltage — Your leisure battery voltage should be above 12.6 when fully charged. You can take a reading by connecting your battery to a multimeter. A voltage below 12.6 indicates that the battery needs to be charged. If you can’t get your battery back up to an adequate charge, it could be the case that it’s drained and needs to be replaced. This is particularly likely if the battery is more than five years old.

  1. Determine if there is one particular appliance draining the battery — If your battery can hold a charge, you should check to see if an appliance is siphoning your power unintentionally. There should be a switch in your caravan or motorhome that cuts out appliances powered through the fuse box. If after hitting this switch you find that your leisure battery still loses charge after a day or two, it could be that there’s an appliance bypassing the fuse box. If this is the case, disconnect the appliance and reroute it through the fuse box.

  1. Check the fuse box — If the battery doesn’t drain when the fuse box is bypassed, you’ll need to check for a faulty fuse. Hook your battery up to a multimeter, take a photo of your fuse box, and pull out all the fuses. Put them back in one by one until you find the circuit that is causing the power drain. Old fuses can sometimes use a rub with sandpaper to help revitalise the connection. Failing that, you’ll need to replace the fuse.

Looking after your leisure battery

Here are some simple ways to help you preserve your battery and prevent any problems from occurring in the future:

  • Don’t discharge more than 50% of the battery — Using up too much of your battery’s capacity without recharging could severely reduce its lifespan.

  • Start the engine at regular intervals when it’s not in use — If your caravan or motorhome is in storage for long periods of time, you can keep the battery in good shape by starting the engine every now and again. We recommend doing so twice per month for 45 minutes.

  • Use a trickle charger — Trickle chargers only deliver a minimal electrical charge to the battery once it’s full to avoid overcharging. Chargers which are just ‘on’ all the time will boil the electrolyte (the de-ionised water you use to ensure the plates in the battery are covered) dry, leaving the battery prone to freezing. You can remove the battery from a motorhome when it’s in storage and leave it on a trickle charger.

  • Use Vaseline — Applying a smear of petroleum jelly around the battery terminals helps to prevent corrosive build-ups by keeping moisture out.

2. Problems connecting to the mains

If you can’t power 240V items in your caravan, there could be a problem with your connection to the mains.

  1. Re-connect your caravan to the mains power supply — Many issues powering your caravan directly from the mains stem from simple connection errors when first setting up. Disconnect your power supply and re-connect using the below method:

    How to hook-up your caravan to the mains

  • Check your Caravan Isolating Switch is at ‘OFF’.

  • Take your caravan electric hook up cable and insert the female-end connector into the caravan inlet. Make sure the connecting cable is uncoiled, as a coiled cable conducting a current can overheat.

  • Insert the male-end plug into the site outlet socket and turn it until locked into place.

  • Switch your Caravan Isolating Switch to ‘ON’.

  • Insert a polarity tester into one of the three-pin sockets in the caravan to check all connections are correctly wired.

  1. Check your electrical demand — Mains hook-ups have a maximum amperage they can reach before the circuit breaker is tripped. If your caravan is demanding more energy than the circuit allows, it could be the reason you’re not getting any power. Tally up the wattage of all your caravan or motorhome appliances. Hook-up points are rated in amperes rather than Watts, so you’ll need to convert the number to see your demand in amps. You can quickly do so following this formula:

    Amps = Watts ÷ Volts

    If your total amperage exceeds the hook-up’s maximum supply rating, consider switching some of your appliances off. It’s also worth noting that some appliances (like fan heaters) demand a higher current to start up before returning to a lower one, so you should activate these appliances first.

  1. Check for faults with the socket — If you can rule out any overloading but your supply keeps tripping, you can check whether there’s a fault with the supply socket. Unplug the hook-up lead and ask the site manager to reset the power. If it trips, then the socket or supply is faulty.

  2. Check for faults with the lead — If there’s no issue with the socket, unplug the lead from your caravan and run a current through it to see whether the fault is in the lead itself. If it trips, there’s a problem with the lead. Important: Make sure the exposed end is in a safe, dry space before doing so.

  3. Check for faults with your caravan’s socket — If the lead doesn’t trip the circuit, unplug everything from your caravan or motorhome’s sockets and switch off the circuit breakers. If the power still trips, then there’s likely a fault in your vehicle’s socket. This will need to be repaired by a professional as it’s dangerous to undertake electrical repairs yourself.

If you can’t fix it?

Sometimes the problem might be more complicated than a simple wiring issue, so you’ll need to have your caravan or motorhome properly serviced by a professional.

Safeguard’s Caravan and Motorhome Insurance policies can cover the cost of repairs for you, so if the issue is too tough, you’re not left out in the cold. Get a quote with Safeguard today and join thousands of happy customers.

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