No high beam on the n/s headlight, dip ok

Noticed that the high beam on the n/s headlight wasn't working, dip ok. Took out the bulb which looked fine but replaced it with a new one and it was just the same, dip but no high. Fiddled with the wires in the connector to no avail. Fuses ok.
If this is a wiring/connector problem? where do the high beam feeds meet to go to the switch?
Or is it the switch? I would think the switch controls both (?) and the feed splits between the lamps.
Earth issue?
To be honest I haven't played with the multi meter yet, just checking here if anyone had seen this before.
It's a 1985 90.
Cheers in advance.

Earth runs both.
Get the meter out, better than guessing.

OK. At he bulb connector on dip setting I get:
blue/white 0V
blue/red 11.8V
black 0V
On high beam setting:
blue/white 0.08V
blue/red 11.6V
black 0V
I traced the blue/white wire back to the connector on the feed side from inside the wing and got dip = 0V, high beam = 0.06V. So it's this feed somewhere...
Started raining again so tomorrow weather permitting I'll check the switch and wires; on an initial look earlier the fuses seemed ok.
Not been a problem until I noticed no high beam the other day.

Are you on glass fuses?
Headlights on separate fuses.check power for both sides.
Take the black eyebrow off you may find crap connections there.

Yes, glass fuses. Pulled them, sanded the terminals and fuse end caps, dab of vaseline, replaced.....
.....now have high beam and dip on both sides
I should have checked the fuse first!
Cheers.