My WDM is for a 1978, but your 1980 is probably the same.

With the slide switch, it's a simple thing. Switch on, power from Fuse #3 goes through switch to two places, one being the OD light on the dash. The other place is the fourth gear inhibitor switch. You should find a red wire under the gear shifter boot that goes down to outside the car, that's the one to the 4th gear switch.

IF that switch is closed, then power gets to the OD solenoid and thence to ground. Pretty straight forward layout.

With the toggle on-off system, things are more complicated. You still have the same solenoid and inhibitor switch, but there's a whiz-bang electronic relay in the circuit. It's mounted under the RH center air vent, accessable by removing the glove box.

Power goes from the fuse panel to BOTH the relay and the push button. The other wire from the push button switch goes back to the relay. Then one wire from the relay goes to the green light on the dash, and two wires, a red and a white, go down the shifter well to the transmission. The red one (on the 1984 240) to the 4th gear inhibitor switch, and the yellow one to the solenoid.

So, as Don Foster said, get the WHOLE wiring harness from the donor car. AND the relay. Note that relay for std shift is NOT the same as for automatic.

Good Luck,

Bob

:>)