Fuse Keeps Blowing

I have a 90 GMC or GEO tracker on which i recently changed the column switch (turn signals wiper control box) since the light switch was jammed. turns out the plastic melted and was sezied shut i dont know how that happened though. Anyways replaced it no problem but now everytime i connect the cars battery the fuse for the tail lights keeps blowing. I checked the cars manual and it says it needs a 15A Fuse and everytime i put one in it blows.
Why is this happening? All the wiring for the column switch is done through a harness.
It might also be worth noting i changed the radio the other day to a cd deck but i wired it myself through trial and error since the harness adapter i bought didnt do squat. I took out the radio fuse and tried but the tail lights still kept blowing.

Help? i already got cautioned by the cops for driving without tailights!

try using a 20A fuse. you might be pulling more amps then the fuse can handle...you can do this by adding extra stuff like cd players and lights. because your taillights are spidered into the cd player harness you might be pulling to many amps. just try to use a 20A or even a 25A fuse.