You have to put the voltage sense wire on the load side (house side) of the isolator to compensate for the voltage drop across an isolator. All your loads must also be on that side of the isolator otherwise your loads will be receiving a higher than necessary or possibly too high a voltage that might cause damage to your battery or electronics
The other wire is your field wire which controls your alternators field which controls its output. Don't do anything to this wire, just let it function as is.
The third wire is probably your ignition on wire. The ignition wire is turned on at the key and provides voltage to your regulator
so it can create a field for your alternator.
Another wire is going to be your alternators primary output wire....the largest red wire.
Another wire might be a ground for your alternator, if you have this is, it is usually wired to the engine
block or back to a secure ground wire going back to your battery.
You may also have a ground wire for the regulator
which provides a secure ground.
Most alternators now have internal regulators which means that the wiring
arrangement that you might see is different from alternators with external regulators.