Both headlights out after bulb replacement

2008 Prius with halogen headlights. Car has about 230k.

• Headlamp on the driver's side burned out. Replaced the bulb and both headlamps worked fine. Should have stopped here.
• Since the passenger side would likely burn out soon and the weather will be turning colder, proactively replaced the passenger side headlamp.
• Following replacement of the passenger side headlamp, neither bulb illuminated when switched on. Both parking lights continued to work as normal. Assumed the passenger side socket somehow grounded and blew a fuse. Socket appears a bit rough from age but no burning.
• Checked all fuses - (2) 15A HP-low RH/LH, (2) 10A HP-high RH/LH. All good.
• Checked power to both sides of the fuses. None.
• Replaced the H-LP and DIM relays as part of troubleshooting. No change. No audible/feel relay click when turning on the headlights.
• Visually checked the fuseable link for any signs of failure. All looks fine but did not check voltage. Appears that there is a 40A fuseable link that feeds the headlights. Everything else in the car works ok.
• Turning on the headlamps with the switch results in the headlamp on light illuminating on the dash. Pushing the stalk away turns on the blue high beams light and pulling the stalk toward the driver turns on the blue high beams light. Switch "feels" as normal. No sign of any issues.

At a loss and would like to avoid replacing the switch if there is something else to check first. Appreciate any insight. Thank you.

 

Brief update. I removed the clear plastic cover on the fuseable link section and checked voltages on all sections above and below each fuseable link. 12+ volts verified on all including the 40A "Head Main". I checked the base of the relays and the H-LP relay has 12+ volts on two of the 4 terminals. The DIM relay, however, has 0 V on any of the terminals. That would sure seem to be the issue but I don't know what is preventing voltage from reaching the DIM relay base.