This is an example of a European style rear fog lamp with red lens. Functionally it will be a big red tail light with higher power bulb (similar to a front fog lamp), wired to a separate switch on the dash, intended to be used during times of foggy conditions. It can be mounted on the rear of an MGA using a back-up lamp bracket or a front fog lamp bracket.

Current part from Moss Motors UK, GAC4608, or from Moss Motors USA, 162-843.