Mesuring Voltage & Amperage of hotend & heated bed

This is my first time posint on the Reprap forum so be nice.

I want to have meter that shows voltage, amperage of the hotend, heated bed & leds.
I do also have a meter that shows the total powerconsumption of the mains power (230v AC).
My problem is with the meters for the hotend, heated bed & leds.
This is the meter i have: https://nl.aliexpress.com/item/33010218601.html?spm=a2g0s.9042311.0.0.44b34c4dIKgd8X
I can not get the meter working correctly by using the scematic shown in the item-discription.

The meter must be powered between 7-110v dc (i use 12v dc of the fan-wires of the extruder).
The +12v dc from a Mosfet goes directly to the hotend.
The returnwire (-12v dc) goes on the richt terminal of the shunt.
The left turminal of the shunt goes to the -12v of the Mosfet.
The thick wires mesure the amperage on the shunt (Positive (Red) left & Negative (Right))
The Yellow wire from the meter goes to the positive of the Shunt.

This is the scematic i use:

The problem is this:
If i turn the printer on, the hotend gets hot and overheates after a few minutes.
I think because the meter gest 12v from the fanwires (from coolingfan) and that goes directly to the hotend.

I try to connect the wires for powering the meter directly to the hotend-wires but then the meter turns ON/OFF if the hotend turns ON and OFF.

I want to have "0.00" on the display when there is no power on the Hotend-wires and Voltage/Amperage value's when the Hotend gets power.
So, the meter must ALWAYS be ON but MUST show the correct values, even if no power is being used.

Does anyone know what i did wrong here?

Thank you

Edited 1 time(s). Last edit at 10/18/2020 06:34PM by VenHeelun.

The MOSFET is GND switched.

When you turn off the MOSFET that GND is disconnected, but you still have a GND through the meter.

I was thinking that the fanwires did power the horend but what you say could also be the case. Question: how do i mesure without powering my hotend and not turn off the meter when no voltage is applied to the hotend? A correct scematic would be nice.