I saw this on audifans.com and remembered some postings here about this
1987 Audi 5kTQ
1980 Audi 5k
1962 and '64 Auto Union DKW Junior deLuxes
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From an Audi mechanic. Here is how he solved the problem of poor
radio reception when using the rear defroster on an Avant. The
grid wires on the 01 A4 Avant are on top of the glass, exposed.
'94 100 S Avant
'89 200 TQ, "Bad Puppy" has a new home!
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This one was cute.
2001 Audi A4 Avant (= wagon)
Radio reception poor when using rear defroster.
Run through this: http://www.vma.cape.com/~patrick/temp/91-01-08.pdf
Start running around the rear window defroster grid with a multimeter.
Current runs through it when defroster is on. Test all end points of
grid, good continuity everywhere, no opens. Just for kicks, touch
glass between parts of grid, get very poor continuity, but it's there.
Window looks clean. Spray glass cleaner over rear window while radio
and defroster are on. Reception completely dies. Wipe window off.