I just purchased GE basic wall timer model 15070 and am having trouble getting the clock to work. I have a single wall switch with 2 black wires and a copper ground. My timer has a black, white and red wires. How do I hook them up? I can get the light to work with the manual switch but not with the clock.

Timer black to hot black (feed from breaker panel). This would have been on one side of the original switch.
Timer red to load black. This would have been on the other side of the original switch.
White to neutrals (white) in switch box. If there is no neutral in the switch box, you can't use this timer in this application.

Make certain that the existing wiring follows standard color codes. Sometimes on older installs a white wire can actually be a hot wire for a switch that is not labeled as such. Nowadays it is required to label such 'reassigned' white wires.

If you are unsure, call a professional.