I purchased a used 9117 tach adaprer and it just doesn't work. When it is installed the car won't even run, it tries to run and will run like crap for like 5 seconds and then die. When I take the adapter out, the car runs just fine. Here is the installation instructions I used...
http://www.youtube.com/watch?v=05lFAKN9uy4
Is there something different about the 99' cobra install? I got this on ebay and i'm going to file a claim if I can't get this thing to work.