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.

Have you tested for a feed to the relay main contacts? The fact that the relays click only proves that the control circuit is bringing in the main contacts if they don`t have a feed nothing else happens.
Do you have a feed out of the light switch in position 2?
Fuses OK?
The latching relay will most likely be to toggle between high and low beam. there should be a feed to this relay with the light switch in position 2 (probably marked terminal 30).
The dim-dip relay`s function is to supply a lower voltage to the dip beams ONLY when the light switch is in position 1 AND the ignition is on. I doubt that this relay is causing your problem as on the 740 which has a similar set up it can be disconnected and the normal lights still work.
Sorry not to be more specific but I don`t have a wiring diagram for the 340. Maybe someone who has will post with more factual advice.
Colin.

[Paul Clifton]

Check the earth has not fell off the dipswitch.If the switch feels a bit 'wobbly' the chances are the bottom retaining screw has fell out which also holds the earth.
Paul.