Well the O/D light flashing indicates that there are codes stored in the computer and they are codes that are related to the transmission indicating there is something wrong with the transmission. I would take it to a ford dealer or tranmission repair shop and have the codes read to see whats wrong. But since the rear light dont work indicates to me there is something wrong with your transmission range sensor or also known as the neutral safety switch. This part is located right on top of the transmission so you need to take off the air intake assembly and just replace the transmission range sensor it shoudl be around $30-$40 for the part. Also these AX4S and AX4N transmission need fresh fluid for them to last long. I replace my transmission fluid every year with mercon v fluid. If I had this problem I would change the range sensor first, but if you dont want to waste time and money go get the codes read. | 
