Easy just pull out the top unit latches to it with 4 inserts.and replace bulb
remove bulb from in side the boot
i have an is300 also and a got a xenon hid kit on my fog lights, they can be replaced , the bulb type is 9006 (hb4)
To replace the dome light in a Lexus IS300, start by using a flathead screwdriver to gently pry the light cover off. Once the cover is removed, take out the old bulb by twisting it counterclockwise. Insert the new bulb by twisting it into place, then snap the cover back on securely. Finally, test the new bulb to ensure it’s functioning properly.
Bulbs can be replaced you have to get bulbs type 9006 (hb4)
Lexus IS300 3rd brake light is changed from the back seat. Pry the light up and disconnect wiring. Replace bulb and put back together. Easy job
To replace the headlamp on a 2001 Lexus IS300, first, open the hood and locate the headlamp assembly. Disconnect the electrical connector from the back of the headlamp and remove any retaining clips or screws holding the assembly in place. Carefully take out the old bulb and insert the new one, ensuring not to touch the glass with your fingers. Reassemble the headlamp by reversing the steps, reconnecting the electrical connector, and testing the new headlamp.
To change the high mount rear brake light on a Lexus IS300, first, open the trunk and locate the access panel on the rear deck where the light is housed. Remove the panel by unscrewing or unclipping it, then disconnect the wiring harness from the old bulb. Replace the old bulb with a new one, reconnect the harness, and reattach the access panel. Finally, test the light to ensure it’s working properly.
this is for the 01 model. it might also be the same for the 03, http://www.porkfist.com/repairs/auto/lexus-is300-taillight.html
To change the low beam headlight on a 2001 Lexus IS300, first, open the hood and locate the headlight assembly. Disconnect the power connector from the back of the headlight bulb and remove the rubber cover. Twist the bulb socket counterclockwise to release it, then pull out the old bulb and insert the new one, making sure not to touch the glass. Finally, reassemble everything by reversing the steps and test the headlight.
2003 Lexus IS300 tail light bulb replacement: Purchase the correct replacement tail light bulb(s) first, before disassembling the vehicle. See sources and related links below for replacement bulb information. Then consult your owner's manual for the tail light bulb replacement procedure. As simple as it sounds, the owner's manual is the best place to start for bulb replacement instructions and illustrations. You may want to consider replacing both left and right at the same time in order to keep brightness and color equal (optional).
To replace the tail light bulb on a 2000 Lexus ES300, first, open the trunk and locate the tail light assembly. Remove the access panel or cover to expose the bulb holder. Twist the bulb holder counterclockwise to remove it, then pull out the old bulb and replace it with a new one. Finally, reinsert the bulb holder, twist it clockwise to secure it, and replace the access panel.
Head to the nearest Lexus dealer that is how they design the car and yes it a shame.