When I got my first mark III my 86.5 I did all the tune up myself and everything else then found someone had taken the check engine light bulb out, so I put it back in. Guess what had a code so I did some looking into it. Turns out the previous owner had a light for ECU power source. He took it to the dealership and I guess they were the ones that removed the bulb. So I asked them what it could be because I had shot all the wires and found nothing wrong. They told me they had never seen that code before. What a rip!!!