Which terminal is ground?
The one labeled +, -, or s?
- spacemissingLv 71 month ago
Either + or - can be "ground",
depending on the way a particular circuit works.
Most worthwhile audio equipment has bipolar power supplies
in which neither + nor - is grounded.
The S terminal is most likely the one that triggers the relay,
so it would not be permanently grounded.
It is best to get connection information from the manufacturer.
When that is not available, you need to find someone who can help you in person.