Audi 80 Type89: fuse 14 always burns through

Hello, I have a problem. And I noticed last time that my numbering lights don’t work. I first thought like lamps would be broken, but then I noticed that fuse 14 (glove compartment, number handle.) burned through. So I switched fuse and it burned out right away. So I measured what resistance I have there between + and -. There are 5 ohms without tacho on it and 3 ohms with tacho on it. I know in the “cold” state it is of course only little meaningful, because the conductivity of the lamps in the luminous state decreases. What can not be true, someone an idea. PS: A year ago I smoked the poti for the speedometer lighting, which I have now bridged (so almost always full on), but also this is not possible.