Back to my hand sketch for a moment:
The readings below are as of a few minutes ago, double and triple-checked. I took them because when I energized the system (after installing a new contactor) I immediately got the desired gusher from the hose bib but, once again, as soon as I tried to activate one of the zones it became a relative trickle.
* A-C and B-C both have good continuity
Voltages are as follow :
* A-B 123V
* A-C 123V
* A-D 0-.117V
* B-D 123V
* B-C 0V
Here's a photo of the inside of the sub-panel (surprisingly, no spiders found)...
And here's one of the new contactor I installed this morning, wired exactly as the original. The two connections you can't see are A-1 (white wire) and A-2, which is jumpered to L3.
I checked carefully for any loose connections at A, B, C and D and found none. I hate chasing parts (fortunately only about $30 so far) and I really don't want to pay a sprinkler guy if I can help it but temps are rising and I have to have sprinklers if I want a lawn.
I think my next step might be trying to test the system (zone) control panel, as I'm not sure how best to proceed otherwise.
_