There are many myths surrounding your 4WD and camper trailer’s electrical system and how it works. How many times have you been arguing with your mates about how to wire a set of lights or an inverter into your setup? Or what deep-cycle battery is right for your needs?

The basic principles of 12V power are relatively simple but can still be very confusing to most of us. In this two-part article, let’s bust 20 of the most common myths about your 12V system, including how it works and the best ways to wire up everything from your UHF to an inverter or even a fridge. At the heart of all of these installs is a quality deep-cycle battery, so we’ll take a look at the right ways to hook all these accessories up and ensure that your installation lasts the distances. And don’t miss part two of this series where we go even more in-depth into this topic!

MYTH 1: YOU DON’T NEED A FUSE IF IT’S ONLY DRAWING LOW POWER

FACT: Every connection that goes to any power source like an AGM battery needs to be fused with two exceptions; your winch and starter motor (which are extremely high current devices). You can use top quality inline fuse holders, fuse blocks (if you have multiple circuits to fuse) or circuit breakers. The fuses are there to protect the cabling and the fuse size should be matched to the cable size. The golden rule is this – if you ever connect anything to your deep-cycle battery, then make sure it’s fused!

MYTH 2: RELAYS MAKE NO DIFFERENCE WHEN WIRING UP LIGHTS

Relays are used for two purposes when connecting electrical accessories to your AGM battery, firstly to reduce voltage drop and secondly to protect the switch (or control circuits) from over-loading. Relays require small amounts of current to switch them on (control circuit) and then you’re able to run much larger currents through the relay contacts. Always use a relay when connecting something like a set of spotlights and powering them off your 4×4 battery.

MYTH 3: ANY CABLE SIZE WILL DO

FACT: Cable size is determined by the current required to run through the cable and the length for the cable required. Generally, the longer the cable run the larger the cable needs to be. The further the electrical accessory is mounted away from your 4WD battery or your dual battery system, the heavier duty the cabling needs to be.

MYTH 4: ANY CIRCUIT BREAKER CAN BE USED FOR ANY 12V JOB

FACT: Circuit breakers aren’t used a lot these days when hooking up electrical components to your AGM battery. There are two types of circuit breakers; auto resetting and manual resetting. Auto resetting circuit breakers must be used for electric brake controllers. We will often use manual resetting circuit breakers to protect larger current circuits where a fuse will not suit. Always remember to match the correct sized circuit breaker to the equipment you’re powering off your 4×4 battery.

MYTH 5: CRIMPING A JOINT IS AS GOOD AS SOLDERING IT

FACT: Wherever possible, solder, solder, solder! A soldered joint done correctly will never break or corrode or become loose. Not every connection can be soldered, though. Use a good quality crimp terminal – not scotch locks – if you cannot get access to solder a joint. Whenever you’re running any sort of electrical circuit off a deep-cycle  battery, the number one fail point is the connections you make – so make sure you make ‘em good!

MYTH 6: ANY TOOL WILL DO THE JOB

FACT: As with anything, always use the correct tools for the job. One of the biggest problems we see is the use of cheap or incorrect tools which can drastically effect a good connection and the flow of power away from your deep cycle AGM battery. These can be either bad crimping pliers or low powered soldering irons which aren’t hot enough. If you are wiring your own accessories invest in some good quality tools fit for the job.

MYTH 7: IT DOESN’T MATTER WHICH BATTERY YOU RUN YOUR WINCH OFF

FACT: A winch should always be wired off your main 4WD battery. It is an electric motor just like a starter, so it draws large amounts of current. If you run a winch off a secondary deep-cycle battery it will run flat very quickly when winching as it doesn’t get a constant charge the same as the primary battery. Also, most secondary AGM batteries are a deep cycle technology and usually 20% less in CCA (Cold Cranking amps) than a 4WD starter battery. You also run the risk of overloading your battery management system.

MYTH 8: WIRING A UHF IS A NO-BRAINER

FACT: Wiring a UHF radio is relatively easy, as long as it is done correctly. On the power side, it’s simple to run constant power and earth wires from the 4WD battery, but the aerial needs to be wired with a bit more caution. It only takes one strand of the external wire to touch on the centre wire and there won’t be any reception.

MYTH 9: ANYONE CAN FIT A STEREO HEADUNIT, THEY’RE AS BASIC AS THEY COME

FACT: Multimedia head units should wire up to the OEM harness. In the case that looms need to be spliced into, and a proper vehicle schematic should be followed and all joins soldered – especially if you’re going to the 4×4 battery directly to pick up your constant power wire. In newer 4WDs with a CANBUS system that interfaces with all the various computers, the cutting of an incorrect wire can go as far as stopping an engine from firing!

MYTH 10: ALL DEEP-CYCLE BATTERIES CAN BE RUN UNDER THE BONNET

FACT: All deep-cycle batteries are affected by heat and some more than others. The location for an auxiliary battery is often not ideal, exposing an AGM battery to higher than normal heat which reduces performance and life expectancy. Some battery technologies are more heat resistant, for example a conventional lead acid is more heat tolerant than a flat plate AGM. So a conventional lead acid auxiliary battery located behind a headlight with air flow will perform and last longer than an AGM deep-cycle battery located near the turbo!