I'm also guessing you are testing on the orange wire on the 3-pin weather pack, correct? That would be power for the display, and in this case it appears it is wired to a cab power solenoid in the sprayer. It really has nothing to do with the steering system other than powering the display. The SteerCommand gets its constant power through a black 2-pin Deutsch connector on the main battery power cable. The SteerCommand is turned on and off by the Guidance Activation plug which is a 4-pin Deutsch on the display cable. The fact that it is powering up tells me both of these connections are fine.

I'm guessing that the relay that orange wire is connected to in the Hagie wiring is intended to ground that orange wire when the key is off, or your meter is finding ground through another circuit connected to the same relay terminal.  That being said I think this fact and the orange wire with the weather pack connector is not associated with your current problem at all.

Sounds like this is a factory Ag Leader Hagie? They may have used different cabling than the standard cables used for aftermarket installations. If this is the situation, you may have more orange wires than I'm used to and some of the above info may be incorrect for your machine.

I had an ECU-S1 last spring that the first time it was powered up for the season it was giving me a message for a bad MDU cable. This was on an Ontrac 3 which uses the same/similar ECU-S1 as you have. I resistance checked the entire cable and it tested fine. I sent it down to Ag Leader and they found extensive corrosion on the circuit board(s) inside the controller. They ended up replacing the entire controller. I'm leaning towards this being a similar situation. I'd suggest having a dealer set you up with a repair authorization and send it into Ames. Their repair times have been pretty fast lately, at least for displays. A display I sent in last week to have a cracked connector housing fixed was back in a week.