Adding a Master Valve Using Existing Wire Runs

[Gene]

Seems like a popular question these days, see my answer here:

Using same wire for 2 zones

This thread may be of interest to you: Not sure if it would be a cost saving over running a new wire, but it’s an option: https://www.amazon.com/Sprinkler-wiring-doubler-device-without/dp/B07FYWHM3L/