340 lights problem

hi all, ive an f reg 1.4 340. Problem is that it only seems to work on sidelights. with engine running and light switch on '2' i cant get main beam (ie dipped beam) and can only 'flash' main beam. This has happened before but im not sure how i solved it.
status today is: ive replaced relays to fuse box (large silver)and the one inside the fascia to no avail. ive got alive to relays as they click, and ive removed cover from silver one ( this seems to be alatching relay which does appear to be latching) next move will be to short out relay switches, but im at a complete loss as to whats up and find haynes diagram ultra unhelpfull any advice appreciated.
Oh also is it a latching relay and could someone explain the function of the main/dip voltage regulator mounted on the bonnet side bulkhead. I think my problem with resolving all this is that im not certain of the logic of the wiring. thanks for reading and when its sorted ill post back.