Sounds like you have the GE sunsmart timer, and are wiring the timer for single-pole.
Following information does not apply to 3-way timer wiring.
Add a comment if you have different timer.
Start with previous timer:
The previous timer was connected to two wires: Hot wire and Load wire.
Hot wire carries power from circuit breaker.
Load wire connects to fan,light, or motor.
How to wire Sunsmart:
1) Only one wire in the electrical box is Hot. That wire is usually black. Connect black Hot wire to timer-black wire.
2) Load wire connects to timer-blue wire.
3) Timer-red wire is capped off for single-pole wiring.
4) Timer-green wire connects to bare copper wire.
5) Timer-white wire connects to Neutral wire. This will power the timer electronics. The previous timer probably had a battery to power timer electronics. Neutral wires are white wires that are twisted together and covered with wire nut and pushed to back of box.
6) If box does not have Neutral wires, then connect timer-white wire to bare copper ground wire until neutral wire can be run from any nearby outlet box.
7) Try the timer, and if timer does not work, then reverse timer-blue and timer-black.
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