Don't overthink it.
Get a male pigtail for your existing lights. If you have the composite (plastic, aero) lights, they are 9007s on a 2003.
https://www.amazon.com/s?k=9007+pigt...f=nb_sb_noss_1
Read the model number off the bulbs on your composite headlights, order the appropriate pigtails for those too, or use cut-off pigtails from the existing harness from your donor vehicle. You will be connecting all the grounds together, and then running individual hot wires to both high beam and low beam bulbs.
2003s are pretty simple in their headlight wiring. Ground is common between both filaments. Only +12V is switched.
With the headlights off and both bulbs unplugged, get your multimeter and figure out which lead has continuity to chassis ground. That is your common ground wire for both headlights.
Turn the low beams on. You will see +12V between one lead and chassis ground and +12V between that same lead and the chassis ground lead you just identified. Connect the ground and the wire with +12V to your new low beam light socket.
Turn the high beams on. You will see +12V between one lead and chassis ground and +12V between that same lead and the chassis ground lead you just identified. Connect the ground and the wire with +12V to your new high beam light socket.
Dont worry about the colors, use a multimeter and its a 20 minute job.