Switch on indicators use power coming out of the switch to chassis negative for 12 volts.
You have to check power to the terminal going into the switch.
If voltage is low then the power distribution that feeds that switch is defective. How does it test out? Voltage coming in?
Is this a nightmare system where individual wires appear out of nowhere to power each switch? If it is - between the DC fuse panel and the switch panel there is a bad connection.
Usually, behind the FUSE panel factory idiots connect multiple wires to one switch in a halfass manner. Pull each fuse the test the switch for total loss of power. When total loss of power occurs, you have found the villain.
If four wires are connected to one fuse, be cautious and take a cell phone image before disconnecting. I have run into too many folks who disconnect four wires, forget about one then go nuts with the "new" problem.
One step at a time and you will find and correct the problem. Keep the image of Benjamin Franklin in your memory. It makes for great worry beads.