Glad it helped. Like you said the pinout on the Ender 3 V3 board is different than the plug’s layout for the K1 fan. Good find on the back of the board 
On my setup, I cut the plug off the original V3 fan and solder it to the K1 fan, yellow to yellow (signal), red to red (Vc), black to black (grd), green to green (pwm). I would recommend this to most to avoid any confusion.
In your case it sounds like you didnt have the original fan and used the K1 plug which is clever 
just a little color code confusing 
I guess if others did what you did, they could keep the original fan as a backup. I would have to solder again, and would probably buy another K1 fan b/c of the airflow upgrade.
Before cutting the wires i tried to pry out the pins from the K1 plug to rearrange them as well as desolder them from the fan but deciced cutting was easiest.
The K1 Fan is much stronger and a good upgrade. I did some quick overhang tests and did see improvements 
So you now have a better working machine then the original 