Aftermarket speedo

So I bought a cheap aftermarket speedo from e bay. Analogue not digital. When I wire it up, there is only a single negative wire that the high beam, neutral and indicators all go into. The issue I’m finding is that wiring them all up together causes issues, for example if I only touch the negative for the neutral light, the indicator and main beam only come on when bike is in neutral, similarly if I touch the negative for the indicators then the neutral is on permanently.

Any suggestions on how to start unwinding this little conundrum?

Cheers

Aftermarket speedo