Rewiring Vintage Sewing Machines - Resurrecting Vintage Sewing Machines Part 5

Hello everyone.  My goal today is to show others how to replace the rotten wiring we have all ran across when we get new to us machines. I want to demonstrate enough about the circuit that anyone reading will feel comfortable with their ability to pick up the parts and wire and within a couple hours have a safely wired fully functional sewing machine.

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We are going to discuss the basics. My plan is to use as much common language and plain talk as possible, I want to keep my explanations as understandable, safe and simple as possible. My analogies may not reflect the physics of electrical theory. But they will reflect how electricity works, how it can be controlled.  I do not intend to try to teach an electrical class within the confines of a blog post, we will be using a standard 120-volt generic sewing machine as our practice dummy.  It starts out very basic and as we succeed in understanding each step, we will add more steps and eventually rewire a complete machine with a controller and on/off power switches and light switch circuits.   Our practice dummy doesn’t have any extra whistles and bells like low voltage lights or multi-speed motors. Those just add confusion to the circuit that I am going to show you. Maybe we can do a more advanced class and go into more detail at a later date.

Sewing machine wiring circuits are all basically the same design with the idea being to create an electrical path from the source, (the wall outlet) to the power switch,(if available) then it will branch off into two separate circuits. One circuit will go to the Light if available and the other will go to speed controller for the motor.  Here is where my means of explaining the manner in which electricity travels differs from the physics of electricity but it follows the flow of the energy that is carried in the electricity and it is easier to understand the concept at a novice level. We are going to assume that the source wiring is correct and we will proceed under that assumption. Also, we are going to assume that the outlet is polarized and grounded. Older style outlets and plug-ins were not polarized or grounded and they only had two slots in the outlet or two blades on the plug-in. On these early types of circuits, the plugs and slots were the same size and electrically on a standard 120v circuit, they were interchangeable. They were at the time considered adequately safe for use even though from time to time a person could receive a shock if the circumstances were not perfect. As electrical safety evolved so did the standard outlets and plug-ins. The second-generation design consisted of a wider slot on one side of the outlet and a wider blade on the plugin to match. This was done in order to assure the two wires from the electrical panel to the outlet would always be polarized in their function of the flow of electricity. The wide blade would always be the NEUTRAL (white) wire in the circuit, while the narrow blade would be the LINE (black) wire. A copper or brass terminal for the LINE side and a silver terminal for the NEUTRAL side would also identify all of the fixtures (outlets and light sockets). In the current evolution, a third wire was added as a dedicated ground wire identified as a green wire or a bare wire,(no insulation).The third connection is identified by green terminals and its fixture connections or slot is below the original two blades and it is round or (U) shaped.  It is important to acknowledge the changes in the electrical specifications and to understand the purpose for the changes. It is also important to realize that those changes have no relevance as far as increased safety for household appliances not intended to be used in damp wet conditions. Light duty extension cord sets are still available with only the two blade outlets and plugins. The outlets and the plug-ins are not the only parts of the circuit being identified as polarized. The insulation covering the wire is also identified. Sometimes the identifier will be a white or gray stripe running parallel with the wire. This stripe is also called a tracer. Ridges molded into the insulation during the manufacturing process may also identify it. The important thing to remember when using lamp cord or extension cord to repair or replace faulty wiring is simply, wide blade or slot, tracer stripe, and ribbing on the outside of the cord are all Identifiers for the NEUTRAL or N ( white wire).With 120v circuits, it is not uncommon for  N to be referred to as L2. No tracers, or ribbing on the insulation and narrow blade or slot designates it as LINE or L1 (black wire) in the circuit. Now that we know what the wires are, it's time to discuss what they do.

In the simplest possible terms basically, the L1 is the power wire that brings electricity from the source to the OFF-ON switch if the machine is equipped with one. When the switch is in the ON position the electricity passes through the switch and branches off to the motor controller, and to the switch for the light. When it is off it stops all the electricity to the machine. The second switch when in the on position passes the electricity to the light if the machine has a light. The motor controller is a variable switch that doesn’t pass all the available energy thru to the motor until it is pushed to its max limit. That is why the motor will run slow when you barely push the controller and at full speed when you press it hard. That is all L1 does. It provides a path for the electricity that is carrying the energy needed to make the light come on, and give the controller (foot or knee pedal)the energy it needs to pass along to the motor. After the electricity hands off the energy to the motor and the light, It needs to return to the source where the cycle starts all over again. This is what the N or L2 wire does. It provides a path away from the light and the motor back to the source. L2 should not be switched, It doesn’t damage anything if it is and the circuit will turn off,  the preferred method is to leave Neutrals or L2 un- switched and do all the switching with L1. If you get crossed up and L1 gets switched to L2 you will trip breakers, blow fuses and may even see some sparks and smoke. Understanding this method of identifying the wires will make it much easier to keep the wires from getting all crossed up when you are re-wiring any projects, even sewing machines.

Ok now that we are armed with this information. Are you ready to re-wire our test dummy sewing machine? I think we are and if we have problems then we can refer back to the paragraph above and work through the glitch. It may seem a little overwhelming at first but you can sketch out your own schematics to help you keep from getting lost and confused. There are no brownie points for doing it all out of memory. As long as you can understand your own drawings who cares how rudimentary they are. I have even used multiple colors to help me keep track of the different wires in the circuit. And most of my drawings only make sense to me.

So let’s give it a try, We start at the wall outlet or power source. We need a power cord with a plug-in that matches the source. We do not plug anything into the source until we are completely finished with our wiring project.  Ok, our cord matches. Now we need to connect the L1 side of the power cord to one side of the Off- On switch. On the other side of the Off-On switch we need to connect one of the wires from the controller, and one of the wires from the light switch. The other side of the light switch gets connected to the light fixture. Now we go back to the controller, the second wire from the controller will get connected to one of the motor wires.  All of this wiring is from the L1 side of the circuit.

 Connections are made in a variety of fashions, They can be wire-nuts twisted over the bare wires to tie the ends all together. They may be screw terminals, in which case wires are held together by tightening down a screw and pinching the bare ends together or they may even be crimp on connectors that are squeezed into the ends of the wires using special pliers or they may be soldered together and insulated  to keep them from grounding out or shorting together. Regardless of the type of connections used, the important thing is the bare ends must be covered to protect from getting shocked or to prevent L1 and L2 from coming into contact with each other or grounding against the side of the machine.

 We are now ready to connect the L2 side of the circuit.  Starting at our power cord the L2 side of the cord needs to be connected to the unused wire from the motor and the unused wire from the light fixture. This should leave no unconnected wires in our circuit and we should be ready to plug in our power cord. Turn the switches both to the Off position. Plug the cord into the wall outlet and nothing should happen. Turn the power switch to the on position. Nothing should happen here either. Now press on the motor controller and the motor should run at speeds relative to the position of the controller. Release the controller and switch the light switch to the On position. You should have light if the bulb and the fixture is good. If you have light, turn the power switch back to off and your light should go off even if the light switch is in the On position. If you have achieved all the functions as described. You are successful and your machine is fully rewired and ready to serve for many years of happy sewing.

Until next time enjoy your machines your way.   Thank you for reading Laurel, Mississippi!
If you missed any of the other posts in this series be sure to check out the entire resurrecting vintage sewing machines series.  You may also enjoy our other sewing machine posts as well.  Don't forget to sign up for our newsletter to get vintage sewing machine information delivered to your inbox each week and a checklist to help you troubleshoot.

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About Melissa Shields

Mel is a 30 something year old quilter, attempting to balance her old school roots with today's trends. When not sewing or shopping for a new sewing machine Mel enjoys reading, reality TV, and Nascar.


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