As Techman says, the Sonotone has a special plug which should be removed prior to soldering to its terminals, then replaced in the back of the cartridge:
https://www.thestyluslady.co.uk/ekmp...s-1499-1-p.jpg
As a quick and dirty test, you might be able to just push the existing tags on the HMV/BSR onto the Sonotone's plug's terminals, having squashed the with a pair of tweezers first so that they grip.
N.