Electrical Problems with a 2001 Hyundai Accent? OD Blows my ECU/TCU fuse. Why?

I have a 2001 Hyundai Accent GL 1.6L DOHC Auto. If The Overdrive on is not engaged when I start the car it blows the ECU/TCU fuse as soon as I turn the key. If I am driving with the overdrive on and It gets turned of the fuse blows and the car quits. When this happens all I have to do is engage the OD and then replace the fuse and its fine. This is a real pain in the . Nothing has been altered or "fixed" electricaly. Its all factory and stock. Its a 10amp 2 prong fuse. I cant figure out what would cause this. Any help would be great thanks.