My car is the RX model with manual boot opening.
The car user guide tells how to open the boot from inside via the little access panel just above the lock.
Once opened, the trims can be carefully removed from the tailgate to expose the huge amount of wiring! (! courtesy light connector needs to be removed from the plastic trim as you take it off.)
SWITCH ABOVE NUMBER PLATE HAS TWO WIRE CONNECTOR WHICH EXITS THE INSIDE OF THE TAILGATE BODY ON THE DRIVER'S SIDE VIA A RUBBER GROMMET (RED & BLACK FROM SWITCH – PURPLE & WHITE FROM LOOM).
DISCONNECT THIS CONNECTOR & CHECK FOR CONTINUITY OF SWITCH TERMINALS WHEN ACTIVATED (NO CIRCUIT FOUND).
WITH LOCK IN CLOSED POSITION, SHORT ACROSS LOOM TERMINALS TO CONFIRM FAULT BY MAKING LOCK RELEASE.
TO GET AT THE SWITCH REMOVE THE 5 NUTS HOLDING THE TRIM PANEL ABOVE THE NUMBER PLATE AND PUSH THE WIRE & GROMMET THROUGH THE HOLE AND RELEASE THE WHITE PLASTIC LUG NEXT TO IT. YOU CAN THEN REMOVE THE 2 SCREWS THAT HOLD THE SWITCH IF NECESSARY.
I FOUND BROKEN/CORRODED WIRE VERY CLOSE TO THE SWITCH & SOLDERED IT. LOOKED LIKE THIS HAD BEEN TAPED PREVIOUSLY!
THEN JUST A MATTER OF PUTTING IT ALL BACK TOGETHER - JOB DONE!
JUST OUT OF INTEREST LEXUS WOULD HAVE CHARGED £95 JUST TO DIAGNOSE FAULT.
LEXUS PART No.84840-21010
£61.62 (INC VAT)