Car won't start sometimes

Hi I have a 89 240sx with a 93 ka24de in it and recently it started having an issue starting sometimes, it was shortly after I relocated my battery to my trunk, I would try to start it and there would just be a click from behind the dash and then if I tried it a few more times it would start, or I would have to go jiggle the battery cables around a bit then it would start. Then yesterday I was hanging out with a friend parked my car for a few hours go to start it and it would not start, I tried to turn it over and I hear a click from behind the dash again and then my electronics wouldn't work either, but they did before I tried to start it, I got a boost and drove it home. I took the battery in they said it was fine, I've tested my alternator with a multimeter and it read over 14 volts, and as far as I understand it that means the alternator is still good, but if I'm wrong please correct me. I've put the battery back in the front for now to see if that helps and I'm gonna double check the terminals now, but I'm not really sure whats wrong so any help anyone could give me would be great, thanks.