I have a Brother Laser Printer HL-5350DN. I refill toner myself but the toner light will not go out. How do I reset it so it goes off?

There is a reset gear in the cartridge that needs to be "reset" or replaced. I've included a link to a PDF file that goes over the procedure to properly refill and reset the toner cartridge. This is a document that is used by a company that does a complete rebuild, so you probably won't need most of the information, just the part on resetting the reset gear.

http://www.uninetimaging.com/downloads/technical/TecArtWebAdded/Brother_HL_5300_Series_tn650_Reman_Eng.pdf

Try the following recommendations from the Brother Support website:

Verify you are using a NEW Brother toner cartridge

Swapping Toner cartridges from one machine to another or installing partially used toner may cause this problem.
Brother machines control their image quality for the most suitable print quality by monitoring the toner's consumption. If you install a partially used toner, Brother machines fail to recognize the toner's consumption correctly and cause this problem.
Therefore if you replace the toner, please use a brand new toner not a partially used toner from another machine.

Verify you are using a GENUINE Brother toner cartridge

For optimum performance use only new genuine Brother branded consumables specially formulated to ensure top print quality.
Printing with 3rd party consumables may reduce not only the print quality but also the quality and life of the machine. If damage is caused to the drum unit or other parts of the machine as a result of using non Brother branded products, any repairs required as a result may not be covered by warranty.

If you install a new genuine toner cartridge but the "Toner Life End" or "Replace Toner" error message remains, verify the toner cartridge is installed correctly.
Reinstall the toner cartridge following the instructions of the Related FAQs in the end of the page.


Note

Please confirm that you have installed both a toner cartridge and a drum unit in the machine.

Clean the Corona Wire

Please refer to the Related FAQs at the end of this page to see how to clean the corona wire.

Shake the toner cartridges

To distribute the toner evenly inside the cartridge, please shake the toner cartridge gently from side to side.

If the problem continues, the toner cartridge may be defective.

http://welcome.solutions.brother.com/BSC/public/eu/gb/en/faq/faq/000000/002500/000017/faq002517_000.html?reg=eu&lang=en&c=gb&prod=hl5350dn_eu&page=FaqEndPage