Piece of kit, coat on seen with a '70s jumper (5,4)

I haven't cracked this one yet — but the brilliant team at Fifteensquared have:

A charade of SN (‘coat on S ee N ‘) plus ‘a’ plus RED RUM (thoroughbred horse, triple Grand National winner, ’70s jumper’), with a cryptic definition, the k’it’ being percussion instruments.