wiring problems 74 valiant

ok wow i just checked the volts at my battery with the car running it was at 17.1 b4 i turned it off cuz it kept going up i havnt done anything to the car yet except jump it the other night when it died and charge the battery. the alt is putting out 18 volts now not sure about the amps cuz i dont know how to check the amps with this meter it has a dial and volts is the only one i understand. btw my ammeter doesnt look to active it just stays in the middle and only goes negative when i use something with the car off and pushing the brake peddle with the car off makes it go negative too, didnt know power brakes use battery power too?