Typically the +12v (Yellow) goes to always-on battery (so the head-unit always has power avail - to sleep for example).

The Acc (Red) goes to a 12v-when-ignition-is-on so that the head-unit is only on when the car is on.

So yes, you need to connect the Acc.

I have not verified 4C's colours and I long forget the details of my own Joying install, but based on this post for example you should have a yellow and a red on the car side to connect to.

https://www.4c-forums.com/posts/1087933/

This is where a voltmeter comes in handy.

 

Just a tip. I would never just connect wires without testing to make sure you have the correct positive and negative terminals. An inexpensive voltmeter can be bought for around $25 or so and is worth its wait in gold (and burned out electronics). The most useful features.... voltage, polarity +- , and than continuity (does one end of a wire go to another point).

As far as power to the head unit. You would need to have the key turned to the accessory position or the engine started. If it still doesn't work you may have blown a fuse on the head unit or the cars fuse in that particuar circuit (again the voltmeter comes into use here.

Hope I am not insulting you.... perhaps you are already very handy with electronics.... but being a forum we all can learn from the rest of us.

 

Not insulting at all, thank you for the replies! I have ordered a volt meter, my next question is what to do with it 😂
I will also check KarlB's thread, thank you.

 

An easy check is connect your yellow and red together. If the radio turns on then the issue is you need to find the accessory wire that is powered only when the key is turned on, and then connect the red wire from the radio to it.

 

I'll take a look, thanks!

 

Did you ever get this resolved?

 

Yes, sorry! I ended up ordering a Metra 70-1784 wiring harness and installing that, and it worked perfectly.

Link here if you need it.

 

Good to know, thank you.