tail light fuse keeps blowing 07 sr5
 

07 sr5 4x4 39,000 mi. My tail light fuse keeps blowing. It seems intermitant. The first time I noticed this was about 4 months ago, replaced fuse and the new one went out in 2 days. Replaced again and it went after a month. Replaced again and it lasted almost 3 months. This morning on may way to work I noticed no radio/heater control lights and knew it had gone again. Any ideas were to start looking w/out taking it in to the dealer?

Thanks
John