The check engine light has been on for a while so i had it checked and it popped up 2 codes. One was the map sensor, so i replaced it and the other is a code 67. According to the haynes manuel there are 2 code 67's: Neutral drive switch or circuit, or Air conditioner clutch switch circuit. The issue that i am having is when i turn on my ac while either driving or sitting at idle the battery gauge and oil pressure gauge start to drop to almost the very bottom, and the idle starts to spike, then return to normal, then spike, then turn to normal. I have a 1990 GT if that helps out. If anyone has had this problem, or knows how to fix these things could you please help me out!!! Thank you in advance for any replys that you submit, and thanx for the help.