Allbrand Caravan Services

Auxiliary Wire

Generally, when AllBrand installs 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.

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).

Everything You Need to Know About Auxiliary Circuits

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.

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) and not come from other points on the vehicle. This single heavy wire is the most effective option and generally proves to be the most popular.

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 has 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 actuated 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.

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 Considerations Basic Auxiliary Wire Auxiliary Wire with Automatic Switch Basic Auxiliary Wire and Fridge Switch
Means of preventing draw on car battery when stationary Pull the plug out or turn the fridge off when stopped Auxiliary wire cuts off when you turn the vehicle off Fridge switch turns off when caravan is stationary
Plug & socket description Utilises standard 7 pin plug and socket
Advantages Cost effective Automatic cutoff Automatic 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 van N/A $240
Fridge performance on 12V Adequate

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