Sew-Tric motors are found on many sewing machines sold in Britain in 1950s, 1960s and 1970s. They are good quality conventional brushed electrical motors without electronic components, so they are heavy and they don’t quit working to this day. But after some 70 years, they often could use a clean or perhaps a change of carbon brushes. For a look inside a motor, see this previous post, but here we’ll just focus on wiring the connector.
Sew-Tric motors, as well as some Hillman motors, are equipped with a 4-pin connector with the pins arranged in an arch. There is also a lamp mounted on the side of the motor.
The connector is mounted to the casing of the motor and may be on top of it or on the underside. On Hillman motors it may also be parallel to the motor axis rather than perpendicular to it as in this photo.
Regardless of the orientation, the wiring scheme remains the same. It is normally embossed on the lid of the connector.
The earth pin is thicker than the other three pins and is screwed to the metal casing, so it’s easy to spot.
This is the socket, and, just to avoid any confusion, it is male because it’s got pins. The plug with the cables going to the mains and to the pedal is inserted into the socket, but still it is female because it’s got holes that the pins go into. Well, tubes, really.
Here’s the inside of the plug. There is no wiring diagram here, but it matches that of the socket.
The earth tube is thicker than the rest, and there is a little earth sign by the larger cavity meant for it. The cable with 3 cores goes to the mains, and the cable with 2 cores goes to the pedal. If you have a metal-cased pedal, it is better to use a 3-core cable there too, for safety.
The wiring is then as follows, from the top:
- Earth – from one or both cables.
- Mains neutral.
- Pedal neutral.
- Mains and pedal line (live wire).
Good luck! 💥