While browsing eBay for a 12 V power socket, I found two types of cigarette power sockets. Most of these sockets had a warning: “not suitable for cigarette lighters! these sockets can only be used to power up accessories”. Hmm, what’s the difference ? I asked myself. Well, a member of an internet forum provided the information.

To the best of my knowledge, there are actually two different types of socket/outlet in use – one as a cigarette lighter socket, and the other as an accessory power outlet. The most significant difference between the two lies at the bottom of the socket/outlet – a cigarette lighter socket has a bi-metallic clip that acts as the positive contact, the accessory power outlet does not.

When not in use, the cigarette lighter (the device that fits into the socket) is retained by friction between the body of the lighter and clips in the lighter socket – at this time the heating element at the tip of the lighter does not make contact with the clip in the bottom of the socket and no current flows. When the lighter is depressed to the heat position, the element snaps into this clip, closing the circuit so that the element heats and at the same time the clip holds the lighter in the “depressed” position until it has heated enough for the clip to expand and release the lighter, which is, by this time, also hot enough to light the cigarette.

Accessory power outlets lack this bimetallic clip and are often marginally smaller to prevent a cigarette lighter from being easily inserted, there may or may not be friction clips in the sides and the positive contact may also be recessed or have a plastic insulator so that a lighter can not make contact if inserted.

Accessory power plugs are typically slightly smaller in diameter than the cigarette lighter and will have one or more heavy spring loaded contacts on the sides to act as a negative contact and a lighter spring loaded tip in the base to act as the positive contact – shape wise they usually lack the “circular nub” that the lighter has which snaps into the clip, and depend entirely on the side contacts to hold them in place.

Take a closer look at the outlets fitted to your vehicles and you may notice the differences – my Grand Vitara has an accessory power outlet at the back and a cigarette lighter socket on the dashboard and they are different – my cigarette lighter will not fit the accessory power outlet, but, all of my accessory power plugs will, and many of those same plugs are an annoyingly loose fit in the lighter socket and need to be “reseated” frequently.