I have a set of 'vintage' foglights from the UK however they dont come with a wiring diagram. From hooking up a previous set, i used a similar set up to this:



HOWEVER (and hence the question) these foglights only have 1 wire coming out of them. Do i presume that inside the light they are wired to earth via the bolt that attaches to the car???

Is this safe given the mounting point will be exposed to the elements??

It will be fine. Consider the earth strap which earths the engine to the car. It relies on only the thread which is in contact with the bolt to transfer better than 100 amperes. Each for light will transfer about 10 amps or less through the grounded bolt, although this relies on the bare metal about the hole in contact with the bolt and the attaching hardware piercing the paint as you tighten it up.

If you want to be sure, measure the resistance between the 12 volt wire in and the mounting bolt, and then repeat this once the light is attached to the car.

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SooperDooperMiniCooperExpertEngineering

All garage work involves equal measures of enthusiasm, ingenuity and a fair degree of irresponsibility.