Originally Posted by tdpinokc
... on our 2018 Vegas so I installed an inexpensive digital voltmeter next to the so called master switch (wired to coach batteries under step). Now I can tell if the coach is on shore power or coach batteries with a glance at the voltmeter. House batteries fully charged normally show me about 12-12.4 volts. Shore power on and connected indicated 13 -13.4 volts. Flip the store/use switch you will see the voltage change.
Thanks for the inspiration, I took this a bit further on my Vegas... (During a previous mod I added a on/off dimmer for the ceiling lights that tapped the + source of the master switch) ... With this mod the coach now sports a dual voltage gauge I found on Amazon. The gauge has three wires, two +; one for each display, and a ground. A three wire harness was run to the main power relay. In the Vegas 24.1 and likely others, that relay is behind the main power center; four screws and the power center pulls out and out of the way easily.
The Master relay is connects the coach BATTERY'S to the DC electric panel and Converted/Charger). The Master Relay has two external fused circuits on the relay itself, on mine one is red (12v + Battery side), the other yellow (12v + Coach Converter/Charger).
Connect gauges "Main" to the red wire (the fused side)
Connect gauges "Aux" to the yellow wire (the fused side)
Connect gauges ground to ground.
Result: If both voltages are equal and read 13.4 or greater, the main switch is "On", the AC is on, and the batter is charging.
If Aux >= 13.4 and Main < Aux, the Main Switch if Off and AC is on (Red Light On).
If Aux =0, the Main Switch is off and AC is off (Red Light Off)
If Aux and Main are ~= and >= 13.4, Main Switch is on, AC is on (Red Light on).
If Aux and Main are ~= and < 13.4, Main Switch is on, AC is off (Red Light on).
This arrangement tells me the state of the Master Switch as well as the health of the: Fuses on the relay, the Red indicator light, and the Converter/Charger. Pictures below: