I just put a newer (used only 60k on it) motor in my 1990 Z and for some reason i cannot keep the battery fuse from blowing!

Most of the time it blows within a few seconds of me putting it in but every once in a while it will last for a while
I installed the motor myself so there is a possibility that missed a ground or something.I NEED HELP!!!! I really miss driving that car!
PLEASE SOMEONE HELP ME!!!!!!!!!!