So after many days and hours putting in the Arnott C-2278 conversion kit. I went to connect the Negative post on battery to see if Air Compressor that I unplugged was not going to kick on. When I touched the Neg post a big spark and smoke from terminal.
Any Ideas what could be causing it.
All four Air suspension plugs are all tucked away.
Lights in trunk still unplugged and 12v outlet
I still need to install the bypass that comes with the system to override computer.
I have not touched any of the fuses.

2007 E550