Just enjoying one of the episodes of the excellent 1980's Jeremy Brett series from the DVD set. The episode was "The Abbey Grange" and as Sherlock nimbly scales the mantelpiece to inspect the bell wire there's a wonderful (and not particularly fleeting) shot of a brown coaxial TV cable fixed to the top of the mantelpiece with white plastic cable clips at about 00:25:03 to 00:25:10. I've never noticed any other goofs in this series and this one is so obvious I can't imagine how it happened.

OK - here it is. (Slightly nervous about posting images from other people's work)