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K-Rain Timer to Rain Bird ESP: Single Black Wire Mystery Solved

Replacing old K-Rain mechanical timer (big wheel with pins) with Rain Bird ESP. K-Rain has only power cord + single thin black wire (not multi-strand). Six zones exist. Where are valve wires?

Diagnosis: Rotating (Indexing) Valve System

The single wire indicates a hydraulic indexing valve, not electric valves.

How It Works

Controller powers ONE electric valve (via that black wire)
That valve sends water to a rotating indexing valve
Water pressure spins a turbine inside indexing valve
Turbine rotates a hub, pressurizing 1 of 6 outlet pipes at a time
Each outlet = one zone

Conversion to Modern Electric Valves

Install 6 new electric solenoid valves
Feed each of the 6 indexing valve outlet pipes with its own valve
Run 6 zone wires + common to new controller
Abandon indexing valve (or remove)

Alternative

Keep indexing valve, buy a controller that supports it (rare). Converting to standard electric valves is more reliable and uses any modern controller.

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