30 is defo power supply/battery, but this exits the relay via no 87, no 85 and 86 are a live and a earth, doesn't matter which way round as all they do is create a magnetic field that pulls the contacts closed, so joining 30 to 87.
This just means it is a std SPST switching relay, doesn't tell what they are connected to, some other relay types used on cars have numbers that denote equipment that they are used for, but not this one.
tabetha