The following links describe the problem:

http://autorepair.about.com/library/faqs/bl116f.htm
http://www.corral.net/forums/archive/index.php/t-66532.html

The harness is very simple. It plugs in the TFI position and then the TFI gets plugged in at the other end.

The symptoms of the failed/failing TFI according to 2 of my friends are the following.

My Mustang friend had an intermitent problem with the TFI which occured only after the car was running more that 30 minutes(also depending on outside temperature). Symptoms included:

Stage 1. Slightly rough running engine

Stage 2. Engine was slightly cutting out when entering city speeds
after driving in highway

Stage 3. Engine not starting for 20-30 minutes after the car is
turned off after a long drive(30-40 minutes)

Stage 4. Engine stalling while driving on the highway at 40Mph


My 93' Taurus Friend had the car die while driving on the highway and it never restarted. He was "lucky" enough his TFI died alltogether and he didn't have to go through stages 1-3 which drove my mustang friend CRAZY.