1988 nissan 300zx electrical problems.

I have a 1988 nissan 300zx. While I was taking out the stock radio, I seemed to have messed a few things up. The
most important, to me anyways, is the digital dash. On the right hand side of the dash it keeps the miles I've driven.
(What I'm talking about it the miles that people reset after filling the gas tank) It had worked fine beforehand but now
it resets every time I shut the car off. I know to some people that's not a problem, but it's REALLY bothering me that
it's not working now. Another thing is the lights on the roof don't work anymore. That, I don't really care about
because I think it's just shorting somewhere. Also, my hazards no longer work, either. The buttons above and below
the hazard button work, just not the hazards. The last thing I noticed is the ac/heat piece about the radio no longer
displays anything nor do any of the bottoms work. So I can't even turn it on, which isn't too bad, but when it rains
and its hot, it gets hot as hell inside the car.
If anyone knows how to fix any, or all the problems listed, that would be GREAT!