Why does our Volvo S80 burn out its taillights frequently?

[littlebobby]

They're just a simple 1156 bulb, as listed in the manual. They seem to last maybe a month or two so if there's just one burned out, we leave it until time for state inspection.
Thanks for the replies. I check the bulb for a broken filament before I replace it. I'm certain the lens interior is staying dry.

 

[trapper1_CA T]

I would suggest to check your alternator output .....it may be putting out too high a voltage. Top voltage should be high 14 or so