Mmmmmmmmh I think we are talking about different things here.

I changed the one in the front spare wheel compartment, in the 4 x relay holder,

That's not a dim/dip relay, is it round

? I think that's

that's the rad fan relay.

There's two different things you have to think about dim/dip is not the same thing as dipping the main beams.

ie you have a twin filament headlight bulb one filament is main beam and the other is dip beam.

You also have

(on a 1b) dim/dip

(this was added to comply with the Euro legislation that was in force at the time) what the dim/dip does is put both your dim beams in series

(effectively halving the output) which makes them come on dim but only with the light switch in the sidelight position

(first click).

Once on the second position the dim/dip relays are de-enefgised.

There is no main/dip relay on a MK1, that switching is done by the stalk on the steering column.

If one headlight is working on dip and the other isn't then it's either the bulb, bulb holder, wiring or possibly the dim/dip relays.

IIRC the relays are are located in the boot below the liner

(passengers side) they normally have rubber covers on them.
