Most of these outlets state "120 watts Max", but when I put just a 100 watt (8 Amps) load on them they immediately drop about 2 volts, i.e. battery reads say 12.6 volts but the outlet is only receiving 10.6 volts.

The wiring is simply not heavy enough to supply a reasonable current at the required voltage.

Now some people do get away with it ok because when the vehicle is running the alternator lifts the voltage up to 13.9 to 14.5 volts, so at the plug you have around 12 volts, but as soon as you turn the motor off the voltage drops way low.

The simple answer is to fit a much heavier cable (wire) to a new and better outlet, as the cig/lighter outlet is far from the best for good electrical contact anyway, with these it only takes a small bump to disconnect the plug, and when you arrive at destination ‘B’ you find the fridge has been off for hours.

I’ll get to the plug/outlet options in a minute, but the cable is our first priority, now wires ain’t wires, here in Australia we have a weird way of grading cable, the standard cable "Auto Cable" is not what it seems, like if it is marked 6 mm then you will find that it’s only 4.59 mm square, and that’s what really matters, how much copper core it has in square mm², not how thick the overall cable is.

You can do this rewire yourself, and it should cost you only about $45 to $65, and then you will never have a problem.

My recommendation here is to run what is called 8 B&S cable, it’s a single cable of 7.91 mm², run from you battery to where you are going to place the new plug socket, if it is in the back of your car it will be about 4.5 mtrs ($3.95 per mtr), you should also put at the battery a 30 Amp circuit breaker  ($11.60) to protect this cable.

You can run this cable through the body and under sill covers etc, or strap it on top of the chassis rails, the main thing of course is to make sure it can’t rub/chafe through anywhere, and is well protected from sharp corners etc.

The earth return can be just a short length of cable, attached to the vehicle body fitted close to the socket using a nut and bolt with a sand papered ‘bright steel’ contact (don’t forget to paint/protect afterwards), just sticking it under a nearby screw is very bad practice and will not give you the long term sound contact that you need.

Now for the plug/socket etc, if you going to run a compressor type fridge (Waeco, evaKool, Engel, etc) the best fitting I have found for this job is the HELLA type socket ($14.95), and the universal plug ($13.95), these sockets are well made and provide good electrical contact and a positive click in.

The universal plug (fitted standard to Waeco fridges) can be used in a standard cig/lighter socket, and will also fit the HELLA type socket.

If however you are using a Finch/Chescold adsorption type fridge, these fridges draw a constant 10.5 amps and need a heavier connection, here I would suggest the "Anderson" type plug (now only $10.00 each, $20 a set), rated at 50 Amps it’s a sure, safe and easy way to transfer heavy currents.

A real trap for the unknowing is that auto cable is often marketed as 10-amp, 30-amp, 50-amp and so on.

This rating is simply the current it can carry before the plastic cover and the copper core starts to melt. It has no other significance.

It cannot for a moment be assumed that a cable described as '30-amps' can carry even half that over any distance without a totally unacceptable voltage drop.

So it pays to be very aware of the mm² size of the copper in the cable and disregard almost all else.

All of the items I have talked about can be purchased from our shop, or from any of the better auto electrical shops.

Well that’s about it, sorry if this has become a little long winded, but I hope this helps clear up some of the campfire mythology around wire and cable etc.