Analoge module issue

Hello

Is there any Document that explains electrical considerations when wiring analog modules?

background:

We have a problem with an analog module. some +/-10v signals when connecting cause  all channels to get faulty and show 7FFF. We found that signal (-) have a +3v potential towards the module power(-) .we connect the (-)s of signals to (-) of module power and the problem solved. I did this by experience but didn't see it in the documents.Now I am looking for a standard guide to deal with such problems.