How hard wired?

(1) The wire harness to the copper flexi board and you still twist in the bulb holders to contact the flexi board?

or

(2) The wire harness directly to the bulb holders?

If (2), the dual filament brake light / parking bulb holders on 240 sedan from 1986 (?) and newer, with third brake light, puts the white brake light / parking bulb holder on the right and the black on the left (driver side).

#7 fuse on the load side travels from the #7 fuse right side, to the stop light, or brake light switch, through the bulb failure sensor (no, not a relay, has reed relays inside), where it is divided to each the left, right, and high center third brake light.

I'll guess something is:
- shorted
- improperly connected
- improperly grounded (with the dimly blinking bulb failure sensor instrument cluster light when you have the right turn signal on as the turn signals are not routed through the bulb failure sensor)

You may have to bone up on auto electrics with knowledge and tools.

Without images, we cannot conjecture very far on such a modification as with your tail light hard wire foibles.

You've inspected the hard wiring work?
--
Give your brickboard.com a big thumbs up! Way up! - Roger Ebert.