Richieee

2010 Lexus RX450h

A simple current tester keeps giving me results for positive connections in the main fuse box under the hood. But, I cannot get power to flow through a verified working fuse tap.
So I got a multimeter. I verified the multimeter is working, and tested the fuse box connections.
The multimeter is generating negative voltage, so I switched polarity of the leads. Multimeter indicates that the fuse box polarity is Reversed!

How can the fuse box polarity be Reversed?
Am I using the multimeter wrong? Is there something I've overlooked?
Reverse polarity is really BAD! It can fry electrical systems & break fuses.

I checked & the car 12V battery terminals are connected correctly (+)(-). This is a new-ish AGM battery, installed 2021.
10 days ago car had a full manufacturer tune-up. All fine.
Car starts & operates normally.
No Warning lights. No apparent issues.
Can anyone explain this?? How is this possible?? What is going on??

I don't understand how a main fuse box polarity can be Reversed, yet the car still operate normally... I'm at a loss

Gerf