Dim / Autolight Problem

There's also a button on the dash by your left knee that controls auto-high beams to come on and off. The sensor to turn the headlights on and off sits in the middle of the dash under the windshield.

Something odd that I noticed was that when I replaced the 12v battery, its operation was smoother and quicker, at least I was under that impression. So try a reset by disconnecting and reconnecting the battery?

 

Check your battery 12vdc voltage directly or at the jump point. It should be at least 12VDC; your systems will operate down to 11.5VDC - but some people notice odd sensor behavior.
Make sure your sensor is clear; no dash mats or sun shades obstructing your rain/daylight sensor.
If you do a systems reset; you must disconnect the battery for at least 10 minutes. Make sure the windows are down and doors unlocked; so if you mess something up - you'll be able to get into it; also have your stereo head unit access code handy. Do not just disconnect and reconnect the battery; the internal power supply capacitors needs to discharge for a full reset to take place. When or if I do a full reset; I usually take the opportunity to clean off the battery top, check electrolyte levels (if accessible), clean contact points and install anti-corrosion pads.

 

Would a Three have come with auto lights in 2014? I had to mod them into my 2010 IV. Did you, or a previous owner, maybe, mod them into yours?

Seeing that your stalk switch makes different things happen in all the positions, I think your stalk switch works, and the hassle of replacing it would be misplaced. Seems more like it is doing its job in the AUTO position, that is, it is telling the body ECU "auto headlights please", and possibly the light sensor is making the ECU think it isn't dark outside, so the ECU chooses DRLs rather than headlights.

Does anything change if you throw a sock over the light sensor on the dash?

In addition to the headlights outside the car, you should (depending on your dash dimmer setting) be able to notice the instrument illumination switch to dim, when the light sensor thinks it is night out. Also, if you have nav, the map normally switches to its light-on-dark "night mode" at the same time.

If the sensor input doesn't seem to be behaving, getting access to Techstream could be useful, so you'd be able to view the actual sensed light level being reported to the body ECU, and the stalk switch inputs. That can streamline your troubleshooting by a lot, compared to poking at things and guessing.

 

When I read the first sentence and then the second sentence, I end up not being sure I understood. The things in the second sentence, when do they happen?