This post is about wiring repairs for sewing machines. Vintage machines often need wiring repairs. When purchasing a used machine it is a good idea to inspect and test isolation prior to any powered tests.
Suggested wiring and supplies are modern and well proven. Soldering is not used in this post.
Deterioration of insulation: Hard, cracked, gooey, or missing
Out of place wiring changes: Inappropriate, makeshift repairs, wiring errors
Corroded conductors: Conductors black, crusty, broken strands
Missing Parts: Wires, insulators, plugs, controller, cord, lamp, sockets, terminal ends
non-insulated terminal crimp tool
non-insulated crimp terminals #22-18 ring lugs #4, #6, #8, #10, barrel splices
#18 stranded TEW insulation 600V 105 deg C appliance wire
Creative Hobbies rayon covered #18 zip with molded plug
heat shrink tubing 3mm, 6mm, 9mm, 12mm (shrink max is ½) WOER 125 deg. C 600V
hot air tool
Creative Hobbies rayon covered cord with molded end 8’ long is a good machine to make a machine cord. I also use about a 1’ section to wire chrome singer lamps used on Singer 128 and 99, leaving a 7’ cord. Purchasing nice cord ends seems impossible, pre-molded end is great!
Singer machines basically wire the same. Parts, termination styles, wiring lengths vary, but circuit stays same. The universal diagram below is from Sew-Classic.
Heat shrink can be used to re-insulate bare stranded wire where insulation has disintegrated. An example is on Singer 201 potted motors. Motor is removed, to get to internal ends. Wire is cleaned of remaining insulation, it crumbles off, take care not to damage strands in process. 6mm ID heat shring will fit over connector end ring lugs. Make tube slightly longer (1/4” per 5” length), it shrinks a small bit in length. It helps to feed a stiff wire with hook into tubing, to pull wire by lug, thru tubing (stranded wire does not push well). Heat shrink with hot air gun. Hobby style hot air tools are inexpensive and work well. A regular heat gun on low setting works too. A hair dryer is not enough. If new to heat shrinking, do some trials. Learn to heat the shrink tube as necessary, with out excess heat. It will quickly shrink, but will stop, do not try for more, excess heat may damage wire insulation.
It seems original ring lugs break off due to wire fatigue. If wire and insulation are both usable, and sufficient length (3/16”) to strip and add terminal, do that. The hardest part is to remember to slide ~1/2 long, 3mm or 6mm heat shrink on wire first, then crimp. Then slide over crimp and shrink. Ring lug crimps have correct crimp orientation, concave part of crimper, is used on seamed part of crimp barrel. Holding terminal with too, then inserting wire, holding and crimping best way to manage a good crimp.
New replacement wiring can be fabricated for cord, lamps and internal wiring, by crimping appropriate terminals and insulating with heat shrink tubing(s)
A few examples shown below.
Light plug on 1922 Singer 99 in bentwood case.
1/4" plug ends on Singer 128 cord for bentwood case
Singer 201 potted motor wire re-insulated with added outer jacket. Shown un-shrunk.
A barrel crimp used to splice wires. Cover with heat shrink length about 2 times barrel length.
The wiring skills of crimping and heat shrinking are easy to learn.
Terminals make safe, easy connections to screwed terminals. This is especially true for lamp sockets where working room and screw size is small (#4 - #6).
Insulation is removed from (red) insulated terminals, for non-unsulated terminals, when non-insulated are not available.