Why does my timer keep blowing fuses or tripping the circuit breaker?

One or more of the electric control valves has a shorted solenoid, or there is a short in the wiring. If you have a multimeter or volt meter you can check your wiring and solenoids for shorts and continuity.

Otherwise, try switching another solenoid from a functioning valve to see if the problem valve will turn on. If so, replace the solenoid. If not, you may have to replace the wiring.