Blown fuse due to unusual fault
 

This fault occured on my 1973 107 series 350SLC over the weekend and may be of interest to other early 107 owners and possibly many other models, especially from this era.

Symptoms in my case were loss of power windows with ignition on (but they still worked with a door open which was a useful feature on my 107) and difficult cold starting on a car that normally starts easily. Inspection of the fuse box revealed fuse 10 had blown. This fuse also powers transmission kickdown and stop lights (I had not noticed either of these not working) in addition to enabling the power windows and cold start valve. A new fuse did not fail until the brakes were operated so the fault was with the stop lights.

It turned out that one of the stop light bulbs had not only a central solder blob, but an additional solder blob near the edge on the ground connection. With time as the central blob had "settled", the outer blob eventually made contact with the centre contact which on the 107 lamp sockets is brought out to the side. This caused a short circuit which blew the fuse.