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

 

 

Thank you. I watched it. All of it. It was looong. 30 minutes.
Review of the basics. Good stuff: volt vs current; AC vs DC; (+)Positive to (+)Positive & (-)Negative to (-)Negative, Polarity is important...
Yes. Correct multimeter procedure was used, and results show fuse box has Reverse Polarity.

Gerf, any ideas how/why the fuse box polarity is reversed?

*Using your YouTube example; it'd be the same as testing one of the batteries & discovering the polarity was Reversed, the (+) was the (-) & the (-) was the (+).

 

You connected the negative lead to a 12-volt post in the fuse box, connect the negative lead to a ground outside of the fuse box.

There might be no power to the high beam headlight fuse while the lights are off, test the positive lead against the positive stud in the fuse box.

 

It isn't, I thought the example that person gave when testing the batteries for you would make it clear. It doesn't really matter which lead is connected to positive or negative on the meter as long as you remember which is which and test on the the appropriate terminals + or - When you reverse the leads so positive is going to negative/ neg to positive you are changing the direction the electrons flow through your meter and the voltage will be correct mostly but it will be negative. This is only useful on a 12v system if you want to change direction that a fan motor turns or operating a sunroof with a three way switch to run the motor in both directions but it would be manual use only.