Auxiliary Wire

Generally when AllBrand installing an Electric Brake Controller into a rig, we will run an auxiliary as well. This allows the caravan’s refrigerator to run on the tow vehicle’s 12V source whilst you are driving, and the internal lighting of the van to work from the vehicle’s battery. These are standard features on most vans and are definitely worth taking advantage of.

When deciding whether to or how best to use the Auxiliary circuit, give consideration to the following:

What is an “auxiliary wire”?
An Auxiliary is a circuit which runs to the van via circuit breaker from the tow vehicle’s battery, to the trailer plug on the rear of the vehicle. Generally linking to the second pin in the socket, it will match up with standard wiring in the caravan.
What is the current (amperage) requirements of the refrigerator?
As a general rule, a 3-way fridge will have a 150W element fitted which will need a heavy duty wire (at least 6mm, preferably heavier gauge) to work as efficiently as possible. Ideally, this wire will run directly to the vehicle’s power source (via a fuse) andnot come from other points on the vehicle. This single heavy wire is the most effective option and generally proves to be the most popular.
How will I prevent flattening the vehicle’s battery?
Consider this scenario: you’re driving along and find a nice spot to stop off for lunch. If there is no means to stop it happening, the refrigerator will continue to draw power from the vehicle’s battery. Before long, you will have drawn enough power to make it impossible to start the vehicle again when you get back in to leave. To help combat this problem, AllBrand have several options for switching to consider:
  1. Auxiliary Wire, No Switch: When you come to a halt, you will need to physically remove the plug from the vehicle’s socket, or turn off the fridge inside of the van.
  2. Auxiliary Wire with Automatic Switch: The Auxiliary connection is acctuated by the vehicle’s ignition. This option is the most common form of switching today. Many rigs with this type of switching have dedicated batteries in the van to run all of the other 12V gear aside from the refrigerator.
  3. Fridge “Motion Sensor” Switch: This option which relies on the rig to be in motion to allow current to pass to the refrigerator is generally fitted along with an Auxiliary wire. The advantage of this type of switch is that it still allows the use of the caravan’s internal lighting when stopped at a site because they bypass the circuit. This option is especially helpful when there is no in-board battery in the caravan available.

Does the auxiliary wire charge a battery in the caravan?

No. This is mostly because a charging circuit has very specific requirements which are quite different from those of general-use Auxiliary power. This includes much heavier wire (generally twin 10mm gauge runs) and a secondary outlet plug (typically of the Anderson type).

Comparison of Auxiliary Wiring Options

Summary of Auxiliary Wire Options and ConsiderationsBasic auxiliary wireAuxiliary wire with automatic switchBasic auxiliary wire and fridge switch
Means of preventing draw on car battery when stationaryPull the plug out or turn the fridge off when stoppedAuxiliary wire cuts off when you turn the vehicle offFridge switch turns off when caravan is stationary
Plug & socket descriptionUtilises standard 7 pin plug and socket
AdvantagesCost effectiveAutomatic cutoffAutomatic fridge cutoff but retain option to use internal lights
Cost for work on the vehicle (bracket values are assuming we are fitting a brake controller at the same time). Allbrand has the price of hot wire in quoted electric brake fitment.$0$240 ($95)$240 ($0)
Cost for work on the vanN/A$240
Fridge performance on 12VAdequate

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