Turn signal fuse keeps blowing.

[Marcushogun]

I have a 91 k1500 Silverado, has an automatic transmission, and tilt steering. I have replaced the tail light assemblies and boards within the last year. All bulbs are new. I have been having to pull the turn signal fuse in order to put the transmission in drive for quite a while. Up until yesterday, I could put the truck in drive, then stick the fuse in, and the turn signals would work fine. Now, the fuse blows as soon as I put it in, regardless of what position the shift lever is in. I drive this truck for work everyday, so I need to get the lights working properly. Any help would be greatly appreciated.