About 6 months ago, the Bulb Failure Warning Light came on when the brake pedal was pressed. I replaced the lower brake light bulbs when the light first came on(I didn't think of replacing the center bulb). The brake lights worked, but the warning light still came on. I ignored the light until yesterday when my wife said that the light was on constantly. I checked the light last night and it went on and off with the brake pedal.

I was concerned that the light had been on constantly and decided to check all lights this morning. The warning light came on, but the brake lights did not.
When I tested the backup lights, the warning light came on.

I tested all of the bulbs and they were good.

I read the FAQs and called the Volvo dealer to check the price of a new Bulb Failure Warning relay. I was told that it was $144, special order. I asked if there was another possible cause of this problem. I was told that all bulbs in the rear must have either a gold or silver base. The center brake light(which I had never replaced) was silver. The lower brake light bulbs(which I had replaced with 1056LL) were also silver. The taillights, backup lights and fog lights were
gold. I replaced the silver bulbs with gold ones. The brake lights work and the warning light stays off.