I drive an 03 350 7.3. Overdrive light blinking only thing I noticed was the OD would not engage. Did it once while towing. What's the issue?

 

Usually the wires on the column for the switch get chafed and ground out. Real thin wires and plug right on top. They used to sell parts, but now its the whole shift lever, switch and everything. Up here its about 90 bucks. Probably cheaper down there. Easy repair, no special tools required.

 

You need to have the codes pulled. It's nothing but a wild guess without knowing what codes are set.

 

This happened to my truck. Easy fix. If you have no other symptoms than that's probably it. It's really easy to see if you take the steering column cover off. If you have shifting issues you'll need to check for codes.