The response from 7Volvofamily nailed it - wagon lights are quite different from the sedan tail light layout. Actually you wagon owners may be lucky.

No white bulbholder. No "lower outer" location. Pretty straightforward but for the dual-filament bulb in the lowest light, brake and tail lights.

When the bulb failure warning system (henceforward BFWS) relay detects an imbalance between the two paired circuits, it trips and you see the "bulb out" warning light.

Paired circuits are tail lights, brake lights (all three), and low beam headlights. If there is a teeny weeny difference in current draw the warning light comes on.

When you see a quick flash on - off, especially with the brake lights, it often means that a contact somewhere (often on a bulb base) has some oxidation on it. That reduces the current flow but the currect burns off the oxide so the warning light goes out.

Try this on each brake light bulbholder: Remove the bulb and rough up the two base contacts. (I usually rub them a little on concrete driveway). Then clean the three contacts and bend each just a LITTLE towards the back of the car. Look at the places in the lamp bracket, too. Clean those places using a pencil eraser if needed.

Check the tightness of the ground conection and the other connections at the lamp. Usually just pulling off a connector and pushing it back on will get off any oxide.

Good Luck,

Bob

:>)