"I have a Nippondenso model 8162 35 amp one wire alternator"
The diagram is for a 3 wire alternator. If you have a one wire alternator, connect white wire to ammeter as in diagram. omit the red and blue wires at the alternator.
"There is a switched line coming from the back of the alternator. Does this go to the oil pressure switch where the red wire is pictured ... tells the alternator to start charging when the engine is running?" Switched output is from oil pressure switch to alternator, not from alternator to switch. On some one wire alternators you can connect this wire and not have to rev alternator to get it to charge. Depends on how alternator is constructed.
"Charge wire B+ to start solenoid?" black charge wire on diagram to post on start solenoid where big battery wire connects.
"Should the voltmeter positive come from battery or solenoid?" Neither. Volt meter + must connect to a switched source so it will turn off when engine is off, otherwise it will run the battery down.
Ammeter and volt meter are different. Which are you going to use? Ammeter connects as in the diagram. Volt meter negative to ground, positive to switched battery voltage. With volt meter, ammeter could be removed and both post connections tied together.
This diagram appears to be for a diesel since there is no ignition switch indicated. On this diagram, if there is a switched output on key starter switch, connect positive of voltmeter there, if not, connect to fuel gauge/alternator side of oil pressure switch. On a gasser connect to switch with wire going to ignition coil.