How to fit an Anderson plug

Updated October 2026 6 min read

Written by: Tom Crew

March 12, 2023

Time to read 6 min

A caravan fridge has to keep running while you drive, and running it on gas on the move is now considered unsafe. If the fridge runs on 12V, the answer is a dedicated cable from the tow vehicle's battery to a 50A Anderson plug at the towbar.

A 12V socket in the cargo area won't do it. By the time the power has travelled that far through thin wiring, the voltage has dropped too far for a fridge to cool properly. This guide shows how to size the cable, fit the relay and fuse, and mount the plug, step by step.

Skip aheadWork out the cable size for your run

A grey 50A Anderson plug in a flip-cover holder mounted at the rear of a vehicle

At a glance
Connector	A 50A Anderson plug, the standard fitting on most caravans. It carries plenty of current and gives a positive connection.
Cable	Twin-core, run straight from the battery. 6mm auto cable suits short runs and light loads; long runs and chargers need bigger cable — check yours.
Protection	An inline fuse or reset breaker at the battery, on the positive wire. We used a 20A fuse for a fridge circuit.
Relay	Makes the plug live only when the ignition is on, so the fridge can't flatten the vehicle's battery.
Test	With the engine running and the fridge on, the voltage at the plug should be almost the same as at the battery.

Why the fridge needs its own cable

Even absorption (3-way) fridges, which cope with low voltage better than compressor fridges, won't cool properly if the voltage reaching them is too low. The aim is to get as much of the battery's voltage to the fridge as you can, and that comes down to cable size and length.

Australian auto cable is sold by its outside diameter, insulation included. "6mm" twin-core cable has a copper cross-section of only about 4.6mm², which is fine for a short, direct run but drops too much voltage once the run gets long or the load gets heavy. Reaching the back of a wagon or ute is often seven metres or more, and that's where it pays to go up a size.

A dual-cab ute with motorbikes on the tray towing a caravan along a country driveway — The run from the battery to the towbar is longer than most people expect.

Work out the cable size for your run

Pick what the plug will power and how far the cable runs from the battery to the towbar. The calculator gives the smallest common cable that keeps the voltage drop in check, what you'd lose with 6mm auto cable, and whether a 50A Anderson plug is up to the job.

What size cable does your run need?

Pick what you're powering and how far the cable runs. The answer updates as you go.

Estimate only, for general guidance. Read the notes under the result before you rely on it.

What it powers typical draw

Your run

Current draw amps

Cable length, one way metres

System

Allowed drop

3% for fridges and chargers, which misbehave on low voltage. 5% suits lights and pumps.

Use at least

Minimum copper
Drop with that cable
Voltage at the far end
6mm auto cable on this run

Anderson plugs Lugs and crimp terminals Fuses and holders

Before you rely on this

Sizes assume twin-core copper cable, the negative run back to the battery, and the smallest cross-section Australian sellers list for each B&S size. Real ratings vary by brand, insulation, bundling, temperature and installation, so use the rating printed on your cable and in its maker's data.
Undersized or unfused cable can overheat and start a fire. Fuse every positive run as close to the battery as you can, and follow the device and battery manufacturers' installation instructions.
The 50A Anderson check is a rule of thumb, not a rating for your plug. Check the connector maker's figure, and keep plugs clean and fully seated.
Work on 240V mains wiring in a caravan, camper or vehicle must be done by a licensed electrician. If you're not confident with 12V work, have an auto electrician do it.
Results are estimates from simplified assumptions and typical published figures. They are general information only, not professional, technical, legal or safety advice, and they don't take your own circumstances into account.
We work to keep these figures accurate, but we don't guarantee they are complete, current or right for your setup.
Products shown are examples from our range, not a recommendation that they suit your vehicle or setup. Check specifications and compatibility before you buy.
To the extent permitted by law, Camping Australia is not liable for any loss, damage, injury, fine or penalty arising from use of or reliance on this tool. Nothing here limits your rights under the Australian Consumer Law.

What you need

Twin-core cable, long enough to reach from the battery to the towbar by the route you'll take, in the size the calculator gives you
A 50A Anderson plug, with contacts that match the cable size, and a holder to mount it on the towbar
An inline fuse holder and fuse, or a reset circuit breaker
A 12V relay, if you want the plug live only with the ignition on
Eyelet terminals for the battery, crimp connectors for the relay, and a crimping tool to suit

A fuse is the safer choice. Once it blows, the circuit stays dead until you find the fault. A reset breaker keeps tripping and resetting if there's a constant short.

A coil of red and black twin-core cable, a relay with its wiring socket, an inline fuse holder, a grey Anderson plug and two eyelet terminals — The parts for the job: twin-core cable, relay, inline fuse, Anderson plug and connectors.

Fitting it, step by step

Step 1: Feed the wire from the rear

Start at the back of the vehicle, or in the cabin near where you'll tap into accessory power, rather than in the engine bay. Starting at the front means threading nearly six metres of cable through a tight grommet in the firewall.

You can run the cable underneath, alongside or inside the chassis rail into the engine bay, or inside the cabin under the carpet and through the firewall. Underneath is often easier, but the cable must not hang down anywhere or sit where it can chafe.

Twin-core cable being fed under the rear carpet of a 4WD

Step 2: Thread it through to the front

Carry on to the front of the vehicle by the shortest route. From the cabin, you only need to push a metre or so of cable through the firewall into the engine bay to reach the battery. Route it to the battery, but don't connect it yet.

Cable being threaded along the floor beside the front seat

Step 3: Wire in the relay

The relay makes the plug live only when the ignition is on, or in the accessories position, so the fridge can't drain the vehicle's battery with the engine off. Fit it along the cable wherever you can reach a 12V accessory power feed.

Connect the accessory feed to pin 86 and earth pin 85. Cut the twin-core cable, crimp connectors on, and plug the wire from the battery into pin 30 and the wire running to the rear into pin 87. Screw the relay to a surface under the dash or cable-tie it to a loom or bracket, well clear of the pedals and steering column.

A relay being wired in under the dashboard near the pedals

Step 4: Strip the cable at the battery end

Cut back the outer sheath to separate the red and black wires where they'll connect at the battery.

A knife cutting back the outer sheath of red and black twin-core cable

Step 5: Fit the inline fuse and eyelets

Crimp the inline fuse wire to the positive (red) wire, then crimp an eyelet on the other end of the fuse wire to suit the battery's positive terminal. Crimp another eyelet onto the negative (black) wire for the negative terminal.

An inline fuse holder joined to the red wire, with eyelet terminals on the red and black ends

Step 6: Crimp on the Anderson contacts

At the towbar end, crimp the Anderson contacts onto the wires and push them into the plug housing. Check you haven't swapped the positive and negative wires before you go any further.

A long-handled crimping tool crimping a contact onto the end of the cable, with a grey Anderson plug beside it

Step 7: Mount the plug on the towbar

Fit the plug into an Anderson plug holder on the towbar, near the standard trailer connector. The holder keeps dirt and debris out of the connector.

A grey Anderson plug being fitted into a holder bolted under the rear of a 4WD

Step 8: Connect the battery and test

Put the fuse in the holder (we used 20A for a fridge circuit) and connect the eyelets to the battery: positive to positive, negative to negative.

Test the circuit with a multimeter or test light across the Anderson plug terminals, with the engine running and the caravan's fridge operating. The reading should be almost the same as at the battery terminals. If it isn't, the cable is too small for the run or there's a poor connection somewhere, because both show up as voltage drop under load.

The positive eyelet being bolted to the battery terminal in the engine bay

Some modern utes and 4WDs have more complicated power systems that need specialist attention. If you're unsure, or not confident with 12V wiring, check with the vehicle's manufacturer or have an auto electrician do it.

Our take

Fitting an Anderson plug is an afternoon's job, and the step that matters most is the one people skip: sizing the cable for the length of the run. Get that right, put the fuse at the battery, and the fridge in the van gets close to full battery voltage the whole way.

Then test it under load before the first trip, not after the food has gone warm. Everything for the job is in our Anderson plugs, lugs and crimp terminals and fuses and fuse holders ranges. Running a fridge in the car as well? Our 12V fridge setup guide covers batteries, solar and DC-DC charging.

Common questions

What size cable do I need for an Anderson plug to my caravan?

It depends on the current and the length of the run. 6mm auto cable has only about 4.6mm² of copper, which suits short runs and light loads. A typical run to the back of a wagon or ute is seven metres or more, and over that distance a 3-way fridge on 12V or a DC-DC charger usually needs 8 B&S or larger to keep the voltage drop to around 3%. The calculator in this guide works it out for your run.

Why won't my caravan fridge cool on 12V while I'm driving?

Usually voltage drop. If the cable from the battery is too thin for the length of the run, the voltage at the fridge falls under load and the fridge can't cool properly. Measure the voltage at the Anderson plug with the engine running and the fridge on: it should be almost the same as at the battery.

Do I need a relay on an Anderson plug circuit?

It's strongly recommended. A relay switched by the ignition or accessories circuit makes the plug live only when the vehicle is on, so the fridge can't drain the vehicle's battery while the engine is off.

Should I use a fuse or a circuit breaker?

Either protects the circuit, fitted at the battery on the positive wire. A fuse is the safer option, because once it blows the circuit stays dead until you fix the fault. A reset breaker will keep tripping and resetting if there's a constant short.

What does 6mm mean on auto cable?

It's the outside diameter of the cable, insulation included, not the size of the copper. 6mm twin-core auto cable has a copper cross-section of about 4.6mm².

How do I test an Anderson plug circuit?

With the engine running and the fridge (or other load) operating, put a multimeter or test light across the Anderson plug terminals. The voltage should be almost the same as at the battery terminals. A big difference means the cable is undersized or there's a poor connection.