Multiple failures at once,but not all the time: a/c,shift indicator,temp,abs

What is your question?

This happens about 80% of the time I start my car, the shift indicator light is not illuminated, temp gauge does not work, abs light comes on, the MPG reading on the dash goes away, and the a/c does not blow cold air. But other times, everything, works fine... to include temp gauge and a/c condenser. The car will be fine but then out of nowhere those things will happen, but everything else works fine. My thought is there is a short somewhere. I've already checked fuses. Positive battery cable harness looks relatively corroded... could this be the case? I've been trying to figure this out forever and do not have the money to take it in to a shop unless I know what is going on for sure and that I can't fix it myself.