For my '85 745 GLE:

Rear taillights share parking lamp/brake lamp in the lowest quadrant.

Left side pkg/brake lamp works correctly at all times, whether pkg lights are on or off.

Right side brake lamp works ONLY when pkg lights are off.

Right side parking lamp works correctly UNTIL: Apply brakes and right side pkg. lamp shuts off and no right side brake lamp lights. IOW, apply brakes at night, and right side pkg/brake lamp shuts completely off.

Also: Bulb out warning lights with parking lights energized and/or brake application.

Swapped bulbs, swapped bulb holders, wiring looks correct (brown/white to pkg, yellow to brake, black to gnd).

Suspect bulb out relay?

PS: What tool do you guys like to use to access the accessibility-challenged lower nuts securing the lens assembly?

 

I believe I'd be verifying that bulb is getting a decent ground.

 

Make sure routing is correct, grounds are tight and clean, bulbs and holders are tight and clean and deoxed.

You access those two 10mm nuts with long deep socket straight through the access holes--they are there, horizontally from the nuts in question.

 

Thanks, after sending my first post I did see the holes for socket wrench extension access and thanked the Volvo design engineers for yet another welcome maintenance-friendly touch.

After cleaning up the grounds, contact surfaces, swapping bulbs and holders around, and jumpering the circuit from one side to the other, I wasn't getting anywhere with this stubborn problem.

Then I decided to sacrifice the rear fog option and unplugged their gray wires and plugged the yellow (brake) to them. I actually like this better; the brakes illuminate the top of the wagon's lenses, unarguably easier to see, day or night. IOW, now the tops lenses are normally off, day or night, and light up @21 watts (stock brake lamp wattage) by applying the brakes. IMO this is better than original because the perceived contrast from completely off to 21watts is greater than from 5w to 21w (maybe it's 26w combined?).

Ever been behind the new firetrucks and see their (LED?) brakelights? They actually come on somewhat brighter for a fraction of a second, then settle down. Annoying but it does get your attention!

I cannot recall ever using (or remembering it was available) the optional rear fogs.