Some times I have brake lights and sometimes I don't?

Hello,

It sounds like a faulty brake light switch is causing this issue.
The brake light switch is located under the brake pedal lever. When the brake pedal gets depressed, the switch gets triggered and the brake light illuminates.
Over time wear and tear can make the switch malfunction and have corroded or burnt pin(s).

Here is a helpful video:

https://youtu.be/RBCDVfzNQGk

I have attached diagrams for your reference.

Please let me know if you have any questions.
Thank you.