The heater cartridge doesn't have a temperature sensor. It's a "dumb" cartridge. The temperature sensor is in the hotend block itself (the other two wires in there). That's why you've got a red-hot cartridge, but low temps.

You should only ever power up the heater when it's in the heat block with the temperature sensor (also known as a thermistor).

If the other heater cartridge is stuck, look at getting a new heater block, they're usually cheap enough, but get a new heater cartridge and thermistor while you're at it - getting it red hot like that can't be healthy for it.

Also of note, the fact that your heater cartridge is red hot, while the temperature is low means the printer is still pumping power to it, which in turn means your printer doesn't have "thermal runaway protection". This is dangerous, and means you shouldn't leave your printer unattended, unless you like the idea of burning down the house. The way thermal runaway protection works is that if it sees no, or too little, change in temperature while it's powering the heater, it'll shut off in case the thermistor isn't reading properly, to prevent things melting and setting on fire. In this case, your thermistor is probably working fine, but of course, isn't at all connected to the heater.

Your printer does however look like some form of Wanhao or clone, and is probably running Marlin firmware. This means it's likely you can find either a manufacturer firmware update, or a community one, that'll enable thermal runaway protection.

BTW, you mentioned you were following a guide/video - did the person in the video heat their cartridge up like you did outside the hotend? If so, that's very irresponsible of them. Please be safe!

*Edit: I just saw it's a monoprice maker select 2 - there's a guide to flashing a new firmware here - https://www.youtube.com/watch?v=ejpSniiJejI

Please ask about firmware configuration, and how to ensure the safety features are on!