1992 Other Subaru Models electrical/ engine

I own a 92 subaru loyale, mil. 190,000. I have a couple questions about problems that may be related. First: The check engine light was on when I bought it 6 months ago. The previous owner said it was a bad sensor and was nothing serious. The car drove great so I did not think to much of it. Is there a way to determine if it is really just the sensor or a more serious problem? Second: About two weeks ago while driving, the dashboad lights went out along with the tail lights, however the headlights remained on. Since then it has been hit or miss, sometimes the lights remain on other times they never turn on and other times the dashlights/ taillights will flicker on and off. Also the heater has all of a sudden taken much longer (20min) to heat up. I was wondering if these problems are related and if so what is causing them. Third: Two days ago the engine began overheating and when I slowed to a stop it stalled. I read a previous post that suggested a blown head gasket. Is there anything else that could be causing this problem.
Any advise/answers are appreciated, thanks.