Fitting spotlamps with a dim-dip system

Use relays. Wire the relay to the low/hi beam connector or wire itself. When the low beams are on, the set of lights wired on the lows will come on. Ditto for the high beams.

If it's just one set you want for the highs (or lows), use a test light. Turn on your lights and probe to find which terminal/wire is hot for the power feed you'll need. Wire one relay coil terminal here, ground the other. Feed a wire (fused) from your battery to a switch terminal on the relay, continue wire from other switch terminal to light set. Ground light set.

Yes I have done that but the run-dip system sends 4.5 volt to the main beam bulb with the parking lights. This is enough to fire the relay and put the driving lamps.

Hmmm... Maybe a resistor in-line to the relay, then?

Or maybe there's another contact in the light switch you can wire to that's only hot when you physically turn the lights on.

I tried a resistor but the relay just refused to switch - the main light switch seems the best bet - so now to dismantle the steering column!!

Thanks