Just did this for someone in the 200sx portion, thought I'd share it here for easier searching.
!!This is for any headlight system that uses 2 separate bulbs, one for high-beam and one for low-beam. This is not for stock or single-bulb systems.!!
To keep your lows on with your highs, add a standard Bosch-style relay as shown below:
Two things to remember here:
1)+12V means exactly that, go right to the battery with a fused line. This gives you a good power source for the lights.
2)Use a relay capable of the power for both low-beam bulbs. Anything lower and the relay will overheat and fail.
