Using the OBD 2 connector for keep alive power will "work" and cords are sold for this purpose but I'd use a non switched power port / lighter socket / power distribution terminal first.

For an OBD 2 connector,pin 4 is chassis ground , pin 16 is positive, fused, unswitched battery power for test equipment use.

The slight spark won't cause the dash wiring to instantly melt. Look for a fuse that cleared and replace it.