several weird electrical problems and maybe a bad etac please help

my dad bought a 2001 ecliple spyder gt automatic with a 3.0 and a convertible top. he bought it about 4 months ago and weve had nothing but problems with electrical things. it doesnt have an alarm system but it has a remote that unlocks the door and has a panic button. well at first the headlights would start flashing at different times of the day. and it wouldnt do it for days then theyd just start flashing and you had to hit the unlock button not the panic button to make them stop. then he got an engine code saying an o2 sensor was bad and so he bought a new one but he still gets the code and random times. and now while hes driving at night the headlights will go really dim and the motor sounds like its running out of juice. someone told us the etac was bad and if we replaced it that would fix it. im not a certified mechanic but i went to school for it and have done a lot of work on cars and this just stumps me. im not sure what an etac is or does, and what it may control. but it costs 300 for a new one and then u gotta have a shop install it an program it. someone please tell me theyve had the same problem and knows the answer. thanks for any suggestions