no left hand indicator on 1991 sprite alpine?

had a new towbar fitted to 2001 ford mondeo 2.0 petrol at local indespension ,with caravan attatched everything else works except lefthand indicator .meter showing voltage there but will not flash bulb .took a link from right hand flasher from 12n plug and bulb flashed.looked at plug connection really badly corroded so this was replaced, still not working