The gang manifolds are a relatively new thing (and kinda costly too). Since they have to run the plumbing to each zone anyway, they usually run the wiring in the same trench but someplaces, the low voltage wire doesn't have to be in the same trench or the same depth as the pipe. (pipe depth is usually less) .

There are several off the shelf wire detectors (Harbor Freight sells one less than $50)
1. You disconnect hot wire of the questionable zone from the timer inside. You connect a lttle battery powered transmitting device to that wire.
2. The transmitter sends a signal down the wire to the solenoid.
3. A sensor you carry around will follow the wire from where the wiring bundle exits the house down to the solenoid. Beeping as you go, with beeps eighter getting louder and closer together as you stry from or get closer to the wire pathway.

BUT, I saw an ingenious way to do the same thing, using a gas powered engine (lawnmower for instance) and a portable battery powered AM radio.
1. Using an alligator clip, you connect one end of a wire to the disconnected questionable zone wire just as in the above instructions.
2. The other end of the wire is wrapped around the plug wire of the lawn mowerthat sits a ways from where you want to track. Several turns around it. This induces a signal in the attached wire that will run down the zone wire to the solenoid.
3. Using the am radio, tune the radio to an unused station or weak station. 540 was used in the example. Start the lawnmower. The premise is, that the radio picks up the induced signal from the underground wire as static. (earphones would be a plus) The static gets worse the closer you are to the buried line. If it fades, you went past the solenoid or veered off the path.

IF you want to trace out all zones, you disconnect the common from the timer and connect the lawnmower's wire to that, but there are so many commons that may crisscross underground it might prove difficult.
Automobile ignition systems usually won't work. The wires are shielded too well against radio interference.
My problem? I don't own a gas powered lawnmower. My big brush cutting Stihl weedeater might work but it's not good practice to hold the throttle down for an extended period of time if there is no load on it. I'm sure not going to risk burning up my old but good Stihl chainsaw. (My neighbors were amazed that I even have a 'real chainsaw' that big, much less can drop start it and know how to use it at my age.)

I routinely hear the heavy gun fire from Ft Hood and about once a month, see C17s fly low over the house, one after another as they either bring in or take out troops (probably weekend reservists) They fly low enough I can see every detail on the airplane. Maybe it's just 2-3 making practice approaches tho.

A BNSF rail line runs East & West about 500 yards due south from my house. Doesn't bother me, I like trains, but if you look in the google earth image, you can see a big multi line rail yard just East of where I live, as that 1 line splits off into sidings in 2 different locations.. Those are Ft hood's rail sidings. I have more than once, driven down a few blocks and watched 80-100 flat cars go by loaded with US Army equipment. Mostly trucks, trailers and humvees and Strykers but some Abrahms too.

Look closely at that yard. The upper yard is empty but the lower yard sidings are full of empty US Army rail flatcars. (I gave up counting after 200)



Closer:
On the first southmost siding, sits loaded flatcars. About 1000 yards farhter East sits another long line of loaded flatcars.
(I combined them for easy viewing but they are in reality, one behind the other on different East West sidings.



These stay loaded 365/24/7 with components swapped out for maintenance and running to keep everything lubed up and tires from getting flat spots.
This, is US Army's III Corps 1st Army Div Heavy ready force. Loaded,cocked, locked and ready to roll.
What's on the flatcars?
The shadows know.........




(This is just a small part of what is at Ft Hood. The US Army 3rd Inf Div at Ft Carson has a similar ready force loaded as well and 1st Armored Div at Ft Bliss does the same at theirlarge rail yard.)

[This message has been edited by maryjane (edited 07-12-2022).]

I have a retaining wall that needs some attention and like 90% of the retaining walls here, it's made from rail cross ties. I am NOT looking forward to driving dozens and dozens of these 3/8x 12"nails thru cross ties but it has to be done. Not tomention all the 5/8 rebar to stabalize it, driven thru the first 2 layers and into the ground.

(an old nail I pulled out last week. New nails are about $1 ea)

And here I thought movin to town was going to mean an easy life... so far, been nothing but work in 103-107 deg temps.

[This message has been edited by maryjane (edited 07-12-2022).]