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
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