bavis

Hi I have just bought a 1995 Mustang 5.0 GT Convertible,passenger side mirror housing is intact but the glass was missing,ordered new glass which came with a backing plate which is supposed to clip on to the existing assembly then you stick the mirror on to the plate,I checked the glass was for correct car but cannot seem to get the plastic plate to click on to the existing mirror housing HELP Cheers Bavis.I am in U.K.