Have you tested the relay by connecting 12v/ground to the pins the would
> normally go into the silver slots of the socket (the coil of the relay) to
> see that it actually switches?
We have a winner! Thanks to bit, David E. White, Gravis and Fred, I've got a normally operating coolant fan in the Toyota. I used the combined wisdom offered here and hooked up a jumper from ground to the relay pole. Sho 'nough, the fan didn't come on when the relay was properly grounded. I ran the jumper to the terminal on the sensor and the fan was still quite with the ignition key on. I started the motor and waited while it warmed up, and the fan came on as the temp rose! So it was a simple matter of cutting a wire to length and routing it from the sensor to the ground pin of the relay socket.
thanks guys, steve