Battery draining overnight

Ok my battery keeps draining overnight on my 72 dart. I did the light test by removing the battery cable from the neg post and used the test light between the post and the cable and the light came on meaning I have an open circuit. I then proceeded to do the fuse test with the light and there was only one fuse that the light went out on and I believe it was the dome light all the rest the test light stayed on. I have all new wiring from m&h along with a new circuit board so what could be going on. Do I have a ground issue or am i going to be chasing gremlins.