1998 A6 avant . Electric window fault .

sounds like a bad ground on one of the main harnesses. find the points were they connect and clean very good.

YEP SOUND LIKE COULD BE THE FUSES.

just renew the motor the cables are going ,its a complete unit all in one about 80 euros trade

Replace the switch. It has lost connection to the up position.

did you check the fuses 1 st the window switch may be at fault but you should ck the fuses first or a test light to ensure power to the switch and to the motor often the wires going between the door jamb break just from the bending from opening and closing the door you should be able to jump { hot wire the motor to the window if you are confident in doing so very common issue but check the fuses first

fuse, check hand book my guess is 1 window etc is stiff putting extra load on motor.

check the rubber sleeve that has a wiring loom inside that runs from the door shut into the door ,sounds like the wires inside are damaged or the connector is corroded or loose

Isimply put a new fuse box in the car, and check all the electric wire .

This is a common problem with the C5 A6 models. Before you replace the fuse for the windows (I think it's number 14, but i don't have a manual in front of me - Anyway, it's the 10A fuse that's blown!) Look under the back of both front seats and you'll see a light that illuminates the floor for the back seats. Rem ove the light from each seat by prying it out with a flat screwdriver and disconnect both leads. Replace the fuse, and your windows (moon roof and interior lights as well) should now work. The lumbar support causes something to short out the lights. I've tried insulating the lights on mine, but the problem always comes back so I just disconnected them altogether.

sounds like a motor problem, i had this on a mitsubishi lancer, same problem, 2 new motors on 2 windows fixed it