E408 start/stop button, you'll need a new center console cover that has the hole for it
1 - 0.35 mm˛ brown, to ground point on center tunnel
2 - 0.35 mm˛ black/gray, splice to existing black/gray on J519 T32b/1 (basically, interior lighting dimming circuit)
3 - 0.35 mm˛ blue/yellow, to J393 T32e/1
4 - 0.35 mm˛ blue/white, to J393 T32e/3
R137 keyless aerial, in trunk area
1 - 0.35 mm˛ black, to J393 T32e/14
2 - 0.35 mm˛ gray, to J393 T32e/13
R138 keyless aerial, under center console
1 - 0.35 mm˛ white, to J393 T32e/16
2 - 0.35 mm˛ yellow, to J393 T32e/15
R200 keyless aerial, this is in the left door, so you have to run it through the 27-pin plug at the body/door junction
1 - 0.35 mm˛ blue, to T27a/1 to 0.35 mm˛ blue to J393 T32e/12
2 - 0.35 mm˛ gray, to T27a/4 to 0.35 mm˛ green to J393 T32e/11
G605 left door handle contact sensor
1 - 0.50 mm˛ brown, splice to door harness ground line that goes to T27a/23
2 - 0.35 mm˛ green/yellow, to T27a/3 to 0.35 mm˛ green/gray to J393 T32e/32
G606 right door handle contact sensor
1 - 0.50 mm˛ brown, splice to door harness ground line that goes to T27c/23
2 - 0.35 mm˛ green/yellow, to T27c/3 to 0.35 mm˛ green/red to J393 T32e/30
start/stop button - 8K0 905 217 A for A5 or 8K0 905 217 C for S5 (C has red ring maybe?); pick whichever look you want
new center console insert supporting the start/stop button depending on if you have concert (8K0 864 261 E V10 for without Drive Select, 8K0 864 261 G V10 for with Drive Select) or MMI 3G+ (8T0 919 611 L WFX)
handle sensor, same for both sides, 4G8 927 753 B
this kind of lays out the aerials:
https://audi.7zap.com/en/usa/audi+a5.../9/909-909000/
you'll need three aerials, part 10, and three plugs, part 14. Then bolt 11 for the door sensor, bolt 12 for the interior sensor, and nut 13 and cover 15 for the luggage sensor.
As for how to install it all, you should get the workshop manuals from erwin.audiusa.com, pay for a day and get all the PDFs for your VIN. Get them all because you'll never know when a task will have a subtask sending you to another document (such as to install the sensor in the Electrical Equipment document, it's going to send you to remove the interior trim as documented in the Body Interior document, etc).
As for what coding change is necessary in the J393, I don't know. I'm sure it's been documented. And you'll need to look and make sure the J393 in your car has the T32e installed instead of a blank spot.
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