The switch for the optional extra electric fan used to supplement the demisting and fresh air. Fits all models including 1303 & padded or metal dash models. The electric fan was an option M121 fitted to flat screen models at time of order, or fitted as standard on 1303 models. This reproduction switch now includes the locking nut and the knob for a metal dash car - if you have a padded dash or 1303 then you will need knob 113-959-513/A.