The Power Watchdog Bluetooth Voltmeter, # HU37FR monitors the power flowing from the electrical source to the RV for purpose of identifying if the voltage drops to a low level that can damage to the electrical components. It does not meter the usage but rather the voltage range. view full answer...
The Hughes Autoformers AC Digital Voltmeter, # HU28FR that you linked to is for measuring voltage at an operating range between 108 to 132 volts. This is irrelevant of the amperage supply from the pedestal.
If I understand correctly that you are wanting to monitor amps being supplied to your RV, I suggest a surge protector. From Hughes, we have the Power Watchdog Surge Protector, # HU97FR for 30 amp and # HU47FR for 50 amp. The 30-Amp or 50-Amp surge protector offers 6,100 joules of... view full answer...
It does sound like your 2011 Nissan Frontier is missing one of the blue relays; the one that is for the running light circuit. We do have the blue relays in the Curt Relay Kit # C57000. view full answer...