So the simplest way would be to take the low beam wire of the Fiero to the low beam bulb of the headlight and the high beam wire of the Fiero to the high beam bulb of the headlight.
If you wanted the lows to stay on with high beam then you'd need a dual, double pole relay (or wire two double pole relays in parallel)
Notice this setup only uses one Fiero high beam wire to drive things.
When in low beam, the relay(s) are de-energized (as shown) so the power just goes to the low beam bulbs. There's now way for power to get to the high beam bulbs so they are off.
When you select high beam, the relay energizes and the power is now sent to BOTH sets of bulbs.
The nice thing about this setup us that if the relay coil fails, you still get at least your low beams by default.
You'd only need one relay hooked up to ONE of the Fiero high beam wires and just split the output wires of the relay(s) to both sides of the car.
Well, that's how I'd do it anyway.
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Anything I might say is probably worth what you paid for it, so treat it accordingly!
Dave
www.ltlfrari.com