Ahem. This page was the first link I found when I googled "Shimano E-tube light". Yet important info is missing. You don't need to buy the $200 PC tool.
You can access the Light On/Off option in the E-tube phone app by downloading an older version, such as V3.4.3, from an app archive.
This worked for my E7000 and E8000 motors. Not sure about other models.
Google "Apkpure" on your smartphone (need android afaik). Enter the site and search for "Shimano", select the "E-tube Project Cyclist" app, scroll down to "Previous versions" and select "more", select/download "V3.4.3", find the downloaded file on your phone, open it, let it install, done! I did NOT need the Apkpure App to install the download, even though the site tries to tell you that. Once installed, E-Tube V3.4.3 appeared in the Google Play Store library like a normal app. You should turn off automatic updates to prevent it from updating. When you start E-tube 3.4.3 it will try to update to the latest version, so just cancel that update. The Light On/Off option is in the Drive Unit customization. Once Light is On, you can access the Light On/Off setting that was locked on the Shimano Steps Display.
Yes, it's scary to download potential malware from unknown sources. Don't just trust me, google "is apkpure safe" and read what other users have to say. I used an old phone that I didn't care much about to download and so far so good.
I'm so happy I found this. I dodged a bullet. Really hope this will help more people save $200 and a headache <3
Be aware that opening this "lock" on the Light menu will decrease your available battery capacity and range, as the Shimano system apparently calculates and reserves 40 minutes of light from your battery to make sure you don't run out of light on the road. This capacity decrease can be unreasonably large - more than 20%. This is probably the reason the Light menu is locked away on new bikes. Locking the light menu the same way you unlocked it should return the battery and range to normal.
Testing effects on battery range. I have kept very detailed notes on range/distance/time on every charging cycle ever since I got my 500 Wh Shimano e8010 batteries. They are currently on their 80th and 50th cycle.
Just by Enabling the Lights option (without any light installed) the range shown on the display with a full 500 Wh battery changes from 94/71/47 km to 89/67/44 km in eco/trail/boost respectively.
Having gone through 8 charging cycles on my trail bike with lights enabled but without any lights installed, I'd say that the 4 km range reduction looks accurate, although it's hard to tell with the intense and varied riding this applies to.
Having gone through 10 cycles on my city bike with lights (Lupine SL Nano running at 600 lumen) installed and on at all times, the difference is very noticable. In addition to the 3-5 km decrease from enabling lights, having the lights on and taxing the battery seem to decrease the range by an additional 6 km / 15 minutes runtime on average. That's about 1/8, 12% of the total range.
By my logic, a 600 lumen lamp running for 2 hours would consume maybe 2 full power cells, about 20-25 Wh. If the 500 Wh Shimano battery contains 20-25 times that amount of cells, it certainly makes me confused why the battery consumption from the light isn't closer to 4-5%. Maybe the light is bad on battery efficiency, or my preception of light batteries is off somehow.
But yes, for me installing lights has decreased the total range/time by about (4+6) 10 km / 25 minutes. Instead of 2h30m(+-10m) I'm getting closer to 2h(+-10m) runtime in summer conditions.
For me this isn't a big problem as one charge lasts me two weeks. Having no-hassle lights (with low-beam and high-beam) is awesome. Hope this helped you guys!