1. Rear Dome Light - 1 no. (VW Part Number 6Q0 947 291 A)

   Source: AliExpress
   Price: $14.60 + $3.90 shipping

2. Frame for Mounting - 1 no. (VW Part Number 6Q0 867 599 G)

   Source: eBay
   Price: $12.79 + $4.00 shipping

3. Foam Support - 1 no. (VW Part Number 1P0 867 639)

   I was not able to source this item even after a lot of searching, and decided to drop it from the installation process.

1. 4B0 971 993 (1 no.) + N10 318 905 (3 nos.)
2. 893 971 633 (1 no.) + N10 335 807 (3 nos.)*
3. 1T0 972 703 (1 no.) + N90 684 405 (3 nos.)

Source: I sourced item nos. 1 and 2 from Boodmo. They took 70 days to arrive, which was the most frustrating part of the exercise. I later found them available as a much cheaper kit on AliExpress. :Frustrati Item no. 3 was included in the AliExpress shipment of the rear dome light.
*This assumes that you have the stock front dome light in your car. If you are using a different unit, please order the corresponding connector and terminals.

1. 1 mm sq. electrical wire
2. Butt crimps
3. Harness tape
4. Fevikwik/Fevibond

1. Flat-head screwdriver
2. Torx screwdriver with T20 bit.
3. Utility knife
4. Crimping pliers - regular (example)
5. Crimping pliers for terminals (example)

1. Preparing the Harness
   
   
   

   Referring to the above schematic* (adapted from the Drive2 forum thread), prepare the Harness for branching the input for the front dome light to power the to-be-installed Rear Dome Light. Be careful while crimping the terminals, since they cannot be reused. If you have never done it before, buy a couple extra to practice. They are pretty cheap. Also pay attention to the pin numbers while plugging the terminals into the connectors. If you make a mistake, you will need a terminal extraction tool (example) to correct it.

   

   Here is a picture of the harness ready for installation.
   *This assumes that you have the stock front dome light in your car. If you are using a different unit, please use the appropriate pin configuration.

2. Removing the Headliner

   This requires the following items to be removed: front dome light - 1 no., sun-visors (along with the clip brackets) - 2 nos., grab handles - 3 nos., rear headliner trim (the long one between the two C-pillar trims) - 1 no., and one small black plastic locking clip underneath the rear headliner trim. The VW technician whom I consulted said that all the pillar trims would also need to be removed, but I just slipped - carefully! - the edges of the headliner off the top of the pillar trims.
   Once the headliner comes off the roof, take it out slowly through the back of the car to your work area. As a general warning, please be careful while handling the headliner, since it is a delicate part and may develop creases if improperly handled.

3. Installing the Frame
   
   
   

   Mark the centre line of the headliner, and use the Frame as a stencil to mark the outline of the hole required to install it. There is no pre-marked position on the headliner fitted in the Indian Polos (as shown in the pictures in the Drive2 threads). I picked a position that falls on an imaginary line joining the front ends of the rear grab handles. You can also use the headliner of the Vento as a reference, if you have access to one.

   
   Please ignore the outline at the top of this and following pictures.

   Using a utility knife, carefully cut the headliner along the outline. It is advisable to use some kind of support under the headliner during this activity to keep it from bending and creasing.

   

   After ensuring that it fits properly in the hole, stick the Frame to the headliner. I used Fevikwik for this purpose, but Fevibond may be a better option.

4. Installing the Rear Dome Light
   
   
   

   After the glue has dried, insert the Rear Dome Light into the Frame. It has four locking tabs. Squeeze the headliner at the location of these tabs by applying pressure from both sides, until you feel each tab click in place.

5. Installing the Harness
   
   
   

   Using pieces of the harness tape, stick the Harness to the headliner as shown in the above picture. Plug the connector for the Rear Dome Light in. (Please ignore the top part of the above picture. While executing this DIY, I also upgraded the front dome light to the one found in the Passat.)

6. Refitting the Headliner

   Take the headliner back to the car, and refit it by reversing the order of the steps used to remove it. Do not reinstall the front dome light.

7. Connecting the Harness

   Pull the front end of the Harness through the hole for the front dome light. Plug the stock male connector that usually powers the front dome light into the female connector (4B0 971 993) of the Harness. Plug the male connector (893 971 633) of the Harness into the front dome light, and screw it back in place.