glanza faul code 12 headlights causing problem

i have change my dizzy and igniter, and car has been fine for ages, today i was wiring my spots in because the wires were just all taped together, so i found the live that is operated by switch and earthed bulbs then off the body of the car. now when i switch on my head lights my car either nearly cuts out or cuts out. i had this problem with the left indicator if i turned it on car wud die, changed the earth to the body and problem was solved now having similar issue with headlights but ive disconected the spots now and its still doing it :(
 
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