The Bulb Failure Warning Light on the instrument panel was illuminated. When I turn on the parking lights, all 4 tail-lights illuminate as well as the 2 brake lights, without pressing the brake pedal. Pressing the brake pedal illuminates the 3rd brake light (in the window), while the 2 brake lights remain "on", as do the all tail lights. Same symptoms when I turn the headlights "on". I swapped out the red Bulb Failure Warning Switch (BFWS) Part #1362367 with a spare I have on hand, however, the same symptoms prevail: each tail light fully illuminates, and the 2 brake lights when the parking lights are turned "on". When the parking lights are turned "off", no lights are illuminated. When the brake pedal is depressed, the 2 outside parking-lights (not the brighter brake filament) and the 3rd brake light all illuminate.

I checked black ground wires at each tail lamp assembly. I checked wiring contacts where the harness plugs into the circuit board. I made sure the "ears" of each dual-filament "1157" bulb are seated properly in the holder, and the tabs on the bulb-holder contact the circuit board. (The replacement bulbs are not EOM "Volvo" or "Bosch", rather marked "Made in Brazil".) The 2 rear fog-lights work fine, as do the turn signals, back up lights and license plate lights. The fuse block indicates #15 8A fuse for left-side and #16 8A fuse for right-side. Fuses and contacts are free of corrosion.

I have a test-light and limited electrical knowledge. Any ideas what is causing this "bleed-over" problem, where-else I should check, or what I may have "missed" in my diagnosis? Should I search for a shematic?
Thanks
Marc