The most common cause of "no sound" on a 2012 MacBook Pro running Windows 10 is installing Windows in rather than Legacy (BIOS) mode . Older Macs typically do not expose their audio hardware to Windows when booted via UEFI. ⚡ The Quick Fix: Legacy Boot Requirement
If you are in a rush, here is the TL;DR for the fix:
If the headphone jack has a red light, the system thinks a digital optical cable is plugged in. Try plugging and unplugging headphones several times to "reset" the physical sensor.
You’ve just finished wrestling Windows 10 onto your trusty MacBook Pro mid-2012—the unibody warrior, the last great upgradeable Mac. The one with the glowing Apple logo you could actually pop off with a spudger. You installed Windows for that one piece of legacy lab equipment, or maybe just to play an old game. The install went perfectly. The USB ports work. Wi-Fi? Surprisingly solid.
. If it says "UEFI," you may need to reinstall Windows 10 using a "non-EFI" bootable USB (often identified by an orange disk icon with just "Windows" during boot). Manual Driver Installation
Note: This will give you working sound, but the microphone input levels may be low. It solves the "hot" output issue perfectly.