Nissan Repair: Odd Starting, nissan hardbody, aftermarket radio

Question
I have a 1996 Nissan Hardbody 2.4L 4cyl 5 spd. ex. cab that has ran great since I bought it but now its starting to have odd patterns of starting sluggishly more and more after each start, cold or warm. Thinking it was a bad battery I bought a bigger amp one then I had before but the problem seemed to have gone downhill even more. I'm not sure if I should waste time thinking its my starter or alternator(after reading other answers you've given to others with similar problems). I just got an aftermarket radio and new speakers that I am soon to put in. I'm intrigued to find out if when the previous owner put his old radio back in (before selling it and he kept his old aftermarket radio and speakers) he/someone didn't wire it right and therefore some unknown item is draining power. Jumping it makes it start easily so something has to be draining the battery. No lights, fan, wipers are left on at all. Do you have any thoughts on what to do? Thank you for your time.

-Andy

Answer
Andy,

The radio is wired incorrectly.  Nissan has a strange way of having a wire that looks like a ground when the key is off and then it turns into power with the key on.  I would purchase a radio wiring plug made for Nissan and go from there.  Or, you could check the wiring and eliminate the problem.  Again, you will find a wire that is ground when the key is off and power when it is on and I think that is the problem.  I have experienced this on several Nissans that have had a radio install...