H4 is for the main high/low beam, H3 is for the fog lamp, 5W is for the optional city light. You should install a 5W bulb just to keep dirt off the main reflector. If you want, you can wire the city light to illuminate with the park light so there's a faint glow to the headlights. 5W isn't powerful enough to be a DRL.

H4 and H3 bulbs are available in a range of wattages. You probably shouldn't go beyond 70W with the OE wiring. You can go crazy with 130W bulbs or more by now but you'll need relays and heavier gauge wiring and you might risk melting plastic in the headlight housings. 55/65W H4s in properly aimed headlights put out plenty of light.

Sixto
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