Today at Atelier Kaz - ex-Honda R&D, F1, Indy/CART engineer

When people used to smoke a lot, the cigarette lighter was frequently used and some debris were left inside the socket.

In case the lighter body didn’t get released after reaching the optimum temperature or the lighter body was press down continuously without being noticed by the driver, there is a thermal safety fuse involved at the back of the socket.

This can be a melting wire (just like old fusible link at the battery terminal), low temperature spec solder, etc.

On our NSX, it’s using the low temperature spec solder.

Please refer to Fig. 1.

It consists of three parts with low temperature spec solder.
The bullet terminal (white), blade terminal (yellow) and the socket terminal (blue).
The red arrow points to the soldering point.

They are enclosed in a purposely designed heat resistant custard coloured housing.

The photo speaks for itself but basically, if the bullet terminal gets really hot, the solder would melt resulting in open circuit and cuts off the power supply to the bimetal terminal.