It is not the reed switch fused shut like John suspects, or it would light the warning light as soon as you started the motor, regardless of the position of your light switch.

Here's what happens:

Someone works on those awful sedan taillight assemblies trying to get all the lights to work and inadvertently jams the dual filament bulb in the wrong direction, shorts out the tail light circuit (momentarily grounds it), or tries to put the black socket where the white one goes. The 21W brake light (or the short circuit) overheats the sensing coils in the bulb failure relay, causing the isolated windings to no longer be isolated -- shorted together.

Check both fuse 15 and 16, and be sure never to put anything higher rated than the 8A (white) fuses that belong in there. If you can get both sides of your parking lights to come on with either of those fuses removed, you need to test your BFWS.

Test the BWFS in the tail light position by equalizing the current right at the sensor, as shown below. If the light is still on, you need a new one.




--
Art Benstein near Baltimore

"If life were fair, Elvis would be alive and all the impersonators would be dead." (Johnny Carson)