Very simple it's blowing because some part of the wireing is touching ground you need to pull the cord and check every sigle part of it with the it happens it mostly if the wire is expose somewhere is touching the metal I recommend that you can do 2 things pull the old installation and make new wire seal it with black tape all arround so do not happened again or its kinda danger but it works,... Unplug your (+) on your battery then get a higher fuse like 30a then as soon you get it in plug battery conector back and on seconds you would see smoke some where unplug realquick the battery and there is your problem !!!