Basically you feed the relays main power direct from the battery and only use the feeble stock supply to trigger the relays.
That way you get 12-13V at the lights, not the 7-8V many Golf2s will have degraded to.
Use fused relays and use two relays for the dip and one for the mains - if your main relay blows you can still drive about, if one of the dips blows you can still get home on one light.
You can either hack off the stock loom and fit appropriate connectors, or plug into the stock loom with connectors through to your new set up.