Lenovo BIOS Hacking
initial dump, needs editing and formatting...
Lifted from the cesspool also known as reddit
SAUCE: https://www.reddit.com/r/thinkpad/comments/5jicwh/flashing_a_custom_bios_onto_my_t420/dbjljmd/
Thanks for the reply, the link you provided worked and I'm currently running the modded BIOS.
Going to leave some information here for anyone googling as it wasn't entirely clear how to flash the modded BIOS and/or if it was safe.
First off, I'm not sure if this matters however, lots of talk online said to flash the stock BIOS first of the same version. If you're going to flash a 1.46 modded BIOS, first flash the stock 1.46 BIOS from the Lenovo website (link provided below to all versions of the BIOS) http://support.lenovo.com/gb/en/products/laptops-and-netbooks/thinkpad-t-series-laptops/thinkpad-t420/downloads/ds018785
However, I had a problem where updating the BIOS beyond a certain point (1.46 I believe?) meant you cannot downgrade your BIOS. As soon as I got my laptop I installed the newest BIOS (1.49). To get around this problem you need to use the following code.
winflash.exe /sv /sd "83ET76WW$01C8000.FL1
It's the "/sv /sd" command that gets around the error message that will pop up if you're trying to downgrade your BIOS. Note the "83ET76WW" part is for the 1.46 BIOS. You will need to use a different code for different BIOS's. The video below explains this all nicely.
[ https://www.youtube.com/watch?v=fR208f0QKuQ https://www.youtube.com/watch?v=fR208f0QKuQ]
Now for flashing the modded BIOS. The exact file name I used is as stated below, encase the link goes down, you might be able to google and find the file elsewhere.
Lenovo_ThinkPad_T420_83ET76WW-83uj28us_NWL_LEN21_ADV_RAM_Speedo_AES_vBios-2170.rar
I'm not sure if you have to use the /sv /sd command again when flashing a BIOS of the same version but I did anyway. As before cd in command prompt into where the folder is for the modded BIOS. Run said code. Voilà, you now have the new BIOS.
- NOTE **
If you're wanting to flash your BIOS to install a non-OEM WiFi card there is a way to get WiFi cards such as the 7260-ac to work without needing the flash.
You have to tape over pin #20 for wireless switch bypass and (possibly) pin #51 for Bluetooth. I've not done much research on this but it seems legit. If you don't feel comfortable flashing (I had no previous experience flashing a BIOS and things went fine for me) you can simply cover the two stated pins with electric tape. I suggest do research before applying this method.
Best of luck.