Can you please help me as I’m trying to install v2 doorbell and getting confused on the wiring. Doorbell has all four colours but only black and yellow were used on the old nest doorbell.
Welcome to the Forum, @prabodh.trehan! 
If you have photos of the “before” situation (ideally prior to the Nest doorbell, when the chime presumably had a “dumb” doorbell button installed), then that would be helpful. Other things that might help:
- What do the wires look like at the location where you plan to install Video Doorbell v2?
- Are you using only a single doorbell button?
- What does the transformer look like?
- Do you have a multimeter and know how to use it? (Doing your own testing with a multimeter is the best way to understand how the wiring traces from the transformer, and it’s helpful for troubleshooting and ensuring that you have adequate voltage, etc., but it’s not absolutely necessary.)
i unfortunately didn’t take a before picture thinking all chime attachments are the same but I can tell you that only black wires were used as seen in the picture. Red wires and twisted and capped yellow and green wires were not used at all. I am trying to install a single button doorbell
That’s helpful information, especially the photo, so thanks! 
What about the other questions, though? I’m still wondering about the transformer. Do you have a photo of that? If possible, it’d be good if you could show the stamped plate (usually) that displays the rated output information (Volts AC and Volt-Amperes) as well as the wires that are attached to the screw terminals. That should give some clues about how your wires probably trace out.
2025-08-25T22:21:30Z Edit: Looking at your photos, re-reading your descriptions, and thinking about this a little more, I believe the yellow wire that you see at the doorbell’s mount plate is just meeting up with another one (where it’s nutted together at the chime) as a “return” path to the transformer. That should create a continuous path and is what would be depicted by the green wire in this image from the Chime Controller Installation Guide:
The actual green wire that it’s bundled with in your setup (where you have green and yellow pairs nutted together in the chime box) is likely irrelevant. It may or may not be connected to anything at the transformer end of the circuit, but what I would expect to see at the transformer is a black wire connected to one terminal and a yellow wire connected to the other terminal.
The outstanding question is which black wire in your chime box goes where. Without testing (ideally doing continuity traces with a multimeter or something similar), you won’t really know which is which, but you can try hooking it up one way and if that fails you can swap them. What should be happening in your situation is that one of the black wires in the chime box comes from the transformer and the other black wire comes from the doorbell. You can try arbitrarily picking one and do this:
Connect one of the black wires and the Chime Controller’s red wire to the chime’s TRANS terminal.
Connect the other black wire together with the Chime Controller’s black wire with a nut.
Connect the Chime Controller’s white wire to the chime’s FRONT terminal.
Then you can connect your Video Doorbell v2’s terminals to the black and yellow wires (it doesn’t matter which wire goes to which terminal on the back of the doorbell camera), configure it in the app (set Video Doorbell v2’s Settings ➜ Chime ➜ Doorbell Chime Type to Mechanical), and test. If it’s not working as expected or if you’re hearing unwanted or extraneous sounds from the chime, then swap the connections of the black wires in the chime box (i.e., move the one from the TRANS terminal to be nutted with Chime Controller’s black wire and vice versa).
Personally, I like testing, because it gives me a better understanding of how my system is working and how it’s supposed to work. It also gives me more confidence in my results when troubleshooting. If you don’t have the tools available for that, though, then you can start with this as a trial and then report back.
Good luck! 
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