This is my first bike ever and this little problem has been holding me back from riding it since it is crucial to check the speed at night. someone please hep a first time rider.
update: so I think I have found the location of the problem by looking at this diagram, I have circled where I think it might be it it is the only logical explanation.

Does anyone have a suggestion on what should I do now? clean connections but with what or maybe just replace wires?