electrics resetting when switched off

Hi, and thanks in advance. New member.
I just purchased a 2000, and I have two problems that may or may not be related. First off, each time I switch the truck off, the dash resets (trip odometer, clock, stereo). There is an aftermarket stereo, which was the first thing I noticed resetting, so I figured the constant DC wire was just not connected to said stereo. Upon further inspection, it is the entire dash and not just the stereo. There's nothing obviously disconnected at the battery.
Second, check engine light came on after about 100 miles. I have a buddy with a diagnostic tool, and I'll be seing him today to try to work that out. I mention this mainly to be sure I'm not leaving anything important out.
Thanks again.

 

make sure ur batter terminals are cleaned and tight. had this happen not to long ago, come to find out, the batter cable was lose.

 

Okay, it's not battery terminals.