KEY=ON, ENGINE=OFF, probe the wires at the Throttle-Position-Sensor with a volt-meter.
The instructions for doing this are in the 1st Gen. "stickies" over at Diesel Truck Resource site.
If your TPS shows bad/dead, many have opted for a dash-mounted potentiometer such that they can dial-in O.D. to suit their requirements.
The ONLY function the TPS controls is over-drive.