Most likely the bulb is the problem, if you do have the correct 5/21W then check connection
Aftermarket brake switch is also a problem you must use OEM.
Wiring and/or Connectors faulty
Wrong Brake Light Bulb installed (21W instead of 5/21W)
Brake Light Bulb(s) faulty
Brake Light Switch (F) faulty.
Check Wiring or Connectors
Check/Replace Brake Light Bulb(s)
Check/Replace Brake Switch (F)
The brake switch is a very common issue and break often.
Still need additional information then please get back to me with the reply button, and not the poor or bad service, this way i can get back to you or suggest another expert if needed.
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A bad rating does not constitute a refund.
If you are not happy or you have sorted out your problem before the answer then please let me know with the reply button .
Kind regards Greg.