Why do i keep blowing turn signals?

Probably have a short in one of them or in your piggy tail

 

becuase its an old truck and you have a short somewhere. You are gonna have to trace your wires. . i have an old truck, i wound up just replacing all my wires and harnesses. to avoid that headache for another 20 years or life of truck. I went a little extreme but you gonnnahave to find out where the wire is rubbing through or grounding out. Get you a multimeter and youtube on how to use it to find a short

 

Start at the light and work your way back looking for exposed wires.

 

Out of blinker fluid?

 

Make sure you're using the correct bulb because they make more than one. I made that mistake. Look at your other one and make sure it matches.
Might be as simple as that

 

Vibration over time. Even though they fit tight they do have some tolerance. And overtime it gets sloppier from it moving ever so slightly with road vibrations, potholes and the like.