To be safe I would use a voltmeter. If you do not have one they are relatively inexpensive to purchase at most automotive stores.
Joe, Joyce , 4 Kids and 3 Dogs.
2004 V-10 Excursion with Hellwig sway bar, Roadmaster Active Suspension, Bilstein shocks and steering stabilizer, Super Duty Tow Mirrors,
3.73 Gears, Reese dual cam, Prodigy brake controller.
2010 Jayco Jay Flight G-2 32 BHDS