In my experience, the lights on the UPCs are about as useul as the "check
engine" light or "service engine now" light in cars. enough to tell you to
look at it, but not enough to tell ou what is wrong. And no 'codes" to pull
to help diagnosis.
I think there are only two things that can be wrong. First and most
commonis reversed polarity at the socket. Neutral on hot side and hot on
neutral side. Or in simpler terms white wire on dark brass screw, black
wire on bright silver screw. Note that the mix up ca be in a different
outlet box than the one where you are connecting the UPS. It could be
futher up the daisy chain.
The other error that the UPC could be picking up is an open ground.
I'm not going to give instructiomns on line because I don't want any
liability if you do it wrong. If you do already knw your way arund AC
branch circuits, both are easy but sometimes tedious tests with a quality
digital multmeter and a pair of Mark I eyeballs, and are eually easy but
sometimes tedious repairs.
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