It sounds right to me. Assuming the switch was off so the circuit on the red wire was not getting any power, it would be the same as ground (0V) and when read from the 12 volt side of the battery would be -12V, just like ground would be.

one variable is if it is a positive or negative ground vehicle. most are a negative ground from what i have seen any more. you will have vsd to that switch (voltage source dynamic. that does change since the battery is not the only power supplier. the alternator has quite a range of power that can be generated. on a 12 volt system, you should see from 10.5 on a bad day on up to 15 volts there.

There is apparently a short circuit or a blown fuse between your battery and the wire terminals you were testing. Check your circuit.

The ignition key is off there-for not completing a circuit.

Hi yes it will if it is in circuit as the negative is coming back from the circuit it is attached too.

The tester is protected against polarity inversion.

is it an electronic mm if so it should have read -12. mine does. i dont even pay attention to the color of the probes. might wanna make sure they are plugged in right.

I tested the positive wire red prong of my voltmeter on my red wire and blk prong on neg at bat got 0 for the hell of it I switched it put the blk prong on my red wire and red on red at the battery and it red 12V how or why would this happen