I had similar probs on my 3dr cossie , when i put main beam on the engine coughed & the alternator light glowed, also when indicating the car map thing on the dash used to flash on & off with the indicators, also had rear tail lights diming when indicacting. All my problems were being caused by the multiblock connection underneath the steering cowling where it goes into the ignition switch the block had melted & was causing a drop in voltage (back feeding on main beam). Cut it out & put a more meaty connector in to take the ampage & its all sorted. Just want to renew the ignition switch for a 100% job as it may have done some damage to this aswell but Ford don't do one for a 3dr anymore, only the saff, but 3dr has an extra bit on it for the electric aerial to go up & down when switching ign off/on.

Simon

Good luck mate