I did a similar swap on my '88 B2 from a '92 explorer except I fully used the explorer harness and scrapped my B2 harness. disciplerocks is correct, that is the o2 wire plug. When I first turned my key my worst fear happened.... Nothing! I searched for 2 days throughout the truck and finally found a plug that was only halfway connected on the steering column. After that everything worked fine. Your neutral safety switch prevents you from starting an Auto trans in gear. If the computer doesnt recognize your in neutral or park it will not let the engine fire. Same if you have a manual and there is a sensor to make sure you have the clutch engaged so you don't try to start the truck in gear. You can by pass these switches if you want. If you your trans sensor is connected, then I would search through the harness for loose connections.