Hallo,
the texture channel of the 3D models of two of the search light beams in the gunsUK.dat library file were wrong.
Here's the replacement file; just copy it into SH3's library folder and overwrite the old one.
http://www.mediafire.com/file/r6m31z...4xm/guns_UK.7z
Many thanks to kovall, who found the mistake.