Turn signal

I bought an '81 el camino about 3 weeks ago and the turn signals did not work when I droive it home, I found there was no fuse in it and put one in. The next day however it blew the fuse and has kept on blowing signal fuses since then. I can not get the fuse to blow while the car is not running or while it is in park but as soon as I put it in reverse or past reverse it blows. Any ideas on how to fix this?
Thanks :)