@CHERN This is a weird one...Lets get to the bottom if this.
-to confirm the relay is working simply listen for the audible click when the headlights are turned on. Since your passenger's side ribbon is working as intended I believe the relay is fine.
-Disconnect the 'Driver DRL' wire to ensure that when the parking lights or headlights are turned on the ribbon turns on dim. This will ensure its working without the harness correctly.
*I think our first step is to ensure the Driver Headlight ribbon comes on dim with out the harness involved, then we can troubleshoot from there.*
The line going to the 'Driver DRL' and 'Passenger DRL' are the same connection. There should be no difference between the two sides operation. Once the headlights turn on the relay cuts 12V to the 'Driver DRL' and 'Passenger DRL', this allows the normal dim operation to return.
SRT headlight DRL Mod.jpg