Preparing to Tow

Fit an auxiliary wire to your vehicle to run the caravan refrigerator on 12 volts whilst you are travelling.

In most cases when Hardings install an Electric Brake Controller into a vehicle we will run an auxiliary wire at the same time. This will allow the caravan refrigerator to operate on 12 volts whilst you are driving and the internal lights on the van to work from the car battery. These functions are built into your caravan as standard features and are well worth using!

When deciding whether and how to use the auxiliary circuit in your van consider the following issues and questions.

What is an Auxiliary Wire?
It is a dedicated wire run from the car’s battery via circuit protection to the rear socket of the car. Usually connected to pin 2 at the socket it matches up to standard wiring in the caravan. In a passenger vehicle Hardings usually run the wire internally, on a four wheel drive it is most common to be run inside the chassis rails.

Current draw (amperage) requirements of the fridge.
Your 3 way fridge has a 150 watt element fitted which needs a thick heavy duty wire (minimum 6mm gauge) to work efficiently. This wire should be run directly to the car battery via a fuse and not short cut from other power supply points (e.g. the boot light) This single heavy duty wiring option provides effective fridge operation and is the most popular choice.

How to prevent a flat battery in your car.
If you stop for lunch during your drive you need to ensure that the caravan fridge is not continuing to draw on the car battery. Otherwise it won’t be too long before your car may not start. Hardings have some switching options to help with this. Here is a summary:

  1. Auxiliary Wire, No Switch: When you stop driving you need to either pull the plug out of the back of the car or go into the van and turn the fridge off.
  2. Auxiliary Wire with Automatic Switch: The auxiliary wire is turned on and off by the ignition of the car. This is our most common option these days with many vans equipped with batteries to run the rest of the 12v Equipment, except the refrigerator.
  3. Fridge “Motion Sensor” Switch: This product, normally fitted in the caravan in conjunction with a basic auxiliary wire in the car only allows current to flow to the fridge whilst you are driving. This is our preferred option when you don’t have an onboard battery in the caravan as the fridge is isolated when the vehicle stops however the lights can be used in the caravan when in an unpowered site.

Does the auxiliary wire charge a battery in the caravan?
No, A battery charging circuit has special requirements. Even heavier cabling (8mm twin) is required through a separate socket (usually an Anderson Plug).

See the following table for a summary of Options and Pricing.

Summary of Auxiliary Wire Options and Considerations Basic Auxiliary Wire Aux 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 car off

Fridge Switch turns off when caravan is stationary

Plug & Socket description

Utilises standard 7 pin plug and socket

Utilises standard 7 pin plug and socket

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 car (Assuming we are fitting a brake controller at the same time)

$70

$170

$70

Cost for work on the van

N/A

N/A

$150

Fridge Performance on 12 volts

Adequate

Adequate

Adequate
< Back to Preparing to Tow Index