I"ll give it a try
The speedo cable comes out of the transmission, has it ever been checked?
Rear defroster I assume the switch light works, if not check the relay.
also check the wires on the rear glass for a small break. They sell repair kits at most auto stores.
Anyone ever check the fuel filter?
The cooling fan has a relay under the hood, I would check there first.
I believe the 89 olds speedo is electronic, the torque convertor clutch gets a signal from the speedo telling the convertor to engage at certain speeds and your speedo doesn't work.
My 88 Ciera had a electric plug on the front of the convertor, make sure it is attached securely.