Procedure for replacing Audi A3 arial bee-sting roof mounted amplifier/base for better FM and AM reception with a cheaper Vauxhall P/N

A year after purchasing a second hand Audi A3 Quattro Sport 2003 I've discovered it featured non existent AM reception and the FM reception wasn't that great either.

After a few attempts, I've isolated the problem to the faulty amplifier at the base of the bee sting roof aerial. there is actually a small circuit board inside the bee sting base, which amplifies the AM signal an is powered by the +VDC sent down the antenna core from the Audi head-unit.

The replacement part from Audi costs in the region of £50-60 (OEM: 4B9-051-505 / 4B9051505), so I've decided to shop around. I found a post on the S3 forum about using a Vauxhall antenna base instead:
http://www.s2forum.com/forum/archive/index.php?t-608.html

This part costs around £16-18 as opposed to £50-60, but fits and works just as well in an Audi A3 and is pictured below:
















The S2 post didn't elaborate on the procedure, so I thought I'd documented it for the future. To make the modification/repair, apart from usual screwdrivers and nut drivers, you will need:

• Crimping tool for RG58/RG59/CLF200 and RG316/RG174
• Vauxhall Aerial Base Antenna P/N: 90389799
• RP TNC Male Crimp Connector for Coaxial RG316 RG174

• RP TNC Female Crimp Connector Coaxial RG58 RG59 CLF200

One you have the parts/tools:

1. Unclip the rear passenger roof light from the trim (small flat screwdriver can help) to reveal the mounting nut for the antenna base
2. Unplug the light assembly and put it aside
3. Unscrew the mounting nut to release the antenna base
4. Cut the antenna cable going to the base as close as possible to the base as to leave plenty of cable to work with
5. Remove the old antenna base from it's housing (you could unscrew the two little screws on the base of the unit itself and remove the circuit board to inspect it for problems, corrosion, etc.)
6. Crimp the RP TNC Male Connector to the antenna cable you just cut, see note 2
7. Install the new Vauhall part into the square roof antenna socket/hole and secure with the mounting nut, see note 3
8. Cut the supplied connector on the Vauxhall base and crimp the crimp the RP TNC Female Connector in it's place, see note 2
9. Connect the separate black wire of the base unit to the red cable socket (+10-12V DC) in the passenger light wiring loom you disconnected in step 2 (you should be able to take off the black plastic cover off the black cable to reveal a single prong, which will fit nicely into the back of the wiring loom), see note 1
10. Connect the TNC male and female connectors together
11. Attach the passenger light to the wiring loom and reinstall it into the roof trim
12. Enjoy your newly re-acquired AM reception and Traffic Programming (TP) functions

Notes:

1. The Audi stereo head unit sends around +10-12V DC down the centre pin of the antenna cable, but the Vauxhall apparently does not and requires a separate feed.
2. I could not find the type of socket to match one that came pre-wired with the Vauxhall base, so I decided to replace both connectors for simplicity.
3. Do this step before the crimping, because otherwise you would need to hack the TNC connector to make it fit through the square hole in the roof of the car (I learned this the hard way)