Here is our How to on JDM/EDM Fog Lights on your 2001-2005 IS300.
(2) 6amp Rectifier Diodes (Radioshack $2.99)
1) Remove your back seat.
a.)Lower Comes out first.
b.) 4 12mm bolts hold in the upper.
c.) Once 4 bolts are removed, lift up on the back upper seat.
2.) These are the junctions you will need. Junction 12/13. They will be located on the drivers side behind the back seat.
(The one I am pointing to is Junction 13. This houses the Brake Illumination wires. Green/White. Junction 12 has the Blue Plug above it; this houses your OEM Fog switch Power Wire. Green/Orange)
3.) This is the Power lead from the OEM Fog Switch:
4.) What you are going to do is cut the 2 inner brake light illumination leads. Cut them far enough back so you can solder in the 2 Rectifier Diodes. Then, you are going to strip back the wire on the Green/Orange wire. Use the picture below for reference. This is how its suppose to look:
The Green/Orange is going to power one lead on the Diode. The other lead and the twisted leads will splice into the two Green/White wires.
5.) Lastly, you will need to unpin/cut this wire. Doing this will allow you to use the fogs without the the Illumination Issue Light on your Cluster lighting up.