1432 Becker unit blows receiver-amp fuse

Hello all. My radio in the new mb, purchased from an estate, doesn't work. pulled it had it checked out by a good shop and both amp unit and head unit
ok. tech did find amp fuse blown. (7.5 amp fuse. I think the book calls for a 5 amp.) Put it back in with a new fuse and it blows again. All the head unit does is run the antenna up and down, and accepts the code. When I first coded the radio on the lot, the cassette, fm and am dialogs came up on the display, but since then nothing.
This is a 1991 350sdl with 89K on it, one owner. The owner had the radio fuse wrapped in tin foil, although a good spare fuse was available in the fuse box. I replaced the tin foil fuse, it did not blow when turning on the radio as all other items on that fuse still work.
Also, the owner cut the theft wires on the head unit's pigtail. I don't know if that has anything to do with it.
thanks to all.
Frank Bertrand 84 300td 155K 86 vw diesel golf 193k 91 350sdl 89k 98 Jetta TDI 192K
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