Fiesta electrical problems

[covmutley]

Ive broken the mrs' car!

She has an 1.4 on an 04 plate. Rear brake light went so i simply took out the rear unit, replaced bulb and put unit back. Now, the eadlights come on when braking. Any ideas what has happened? cheers in advance

[covmutley]

fitted bulb with incorrect connectors. was sure i had picked up the right one. thanks for explaining why one affects t'other