Electrical fault on dipped headlight, please help

Hi,

going back a few weeks now i had a warning show up on the dash "right dipped headlight" so i replaced the bulb as you do but this didnt fix the problem. So then i thought wiring fault, traced cables from the headlight back to the cecm behind the dash.The cable for the right dipped headlight didnt have any voltage coming from the cecm with the headlight switch on.So i got a length of cable and connected it to the terminal on the cecm and the battery + andthe headlight works works? If i bypass the headlight switch connecting 12v to the yellow switch wire to the cecm i get the left headlight only? I have replaced the suspected faulty cecm with one from another car and it behaves exactly the same? I cant understand what else could be causing this. Ive looked at wiring diagrams and it looks like there is only 1 switchwire(yellow) from the headlight switch to the cecm. Any help on this is much appreciated.