EDITED TO SAVE YOU THE TROUBLE:
My non-working lights were caused by a keybind conflict that was “tripping a circuit” in the 172. If you are having trouble with the exterior lights not working, check your keyboard and peripheral bindings for one called “Set Electrical Power Circuit Setting”. Make sure it isn’t also bound to anything that affects “Master Battery.”
What was going on for me was, I’d hit the binding for Master Battery and it would trigger the Set Power Circuit simultaneously. If you trigger the Circuit, none of your exterior lights will function. I don’t know of any way to undo that if you trigger it other than restarting your flight.
Many thanks to DementedCorn327 for helping me find my user error.
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Description of the issue:
Pay-ware Cessna 172 Skyhawk - Basic (steam gauge) version has ZERO working exterior lights. Not “dim during the day” like a lot of other planes, I mean they don’t work at all.
[PC Only] Did you remove all your community mods/add-ons? If yes, are you still experiencing the issue?
no mods
FREQUENCY OF ISSUE
How often does this occur for you (Example: Just once, every time on sim load, intermittently)?
every time
REPRODUCTION STEPS
Please list clear steps you took in order to help our test team reproduce the same issue:
- Load up a C172 Basic
- Turn on master battery (starting engine optional)
- Turn on ANY exterior light
- Behold, no lights come on.
YOUR SETTINGS
If the issue still occurs with no mods and add-ons, please continue to report your issue. If not, please move this post to the User Support Hub.
What peripherals are you using, if relevant:
n/a
[PC Only] Are you using Developer Mode or have you made any changes to it?
no
[PC, MSFS 2020 Only] Are you using DX11 or DX12?
n/a
[PC Only] What GPU (Graphics Card) do you use?
4070
[PC Only] What other relevant PC specs can you share?
n/a
MEDIA
Please add a screenshot or video of the issue occurring.
Interior, showing engine running and all light switches in ON position:
Exterior view, showing not a single light is on:
Second exterior view, showing that, unlike the C208B that at least shows a blinking light in the reflection off the surface of the plane, this C172 has no light activity at all:
The latest patch at least made it so the engine will turn on and the plane can be flown, but evidently not at night! Not even a beacon, taxi, or landing light.
I know it’s “just a sim” but not having working lights makes it illegal to fly. It’s certainly not safe, anyway. 
[END OF FIRST USER REPORT]
For anyone who wants to contribute on this issue, Click on the button below to use this template:
Do you have the same issue if you follow the OP’s steps to reproduce it?
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Provide extra information to complete the original description of the issue:
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I edited my most recent reply with the steps.
