Wire & connectorsRebuild shelfHand tools, works as-is

Signal and hookup wire

Also called ethernet pairs, hookup wire, magnet wire, ribbon.

Copper with ordinary insulation, harvested from ethernet, telephone, USB, and the low-voltage harness of a dead machine. Ethernet is the best of them: twisted, plenty of it, decent copper.

If you are new to this category

Wire and plugs are how power and signals move. The insulation is the safety, not the copper. Ethernet cable is fine for small signals and low voltage. It is not a substitute for a power cord. A connector you can unplug is worth more than a wire you have to solder every time.

Match the plug that came with the brick. Center-positive is common and not universal. The drawing on the label is a map: the dot is the center, the ring is the outside.

Center pin and outside sleeve

The drawing on the brick is the polarity. A dot inside a C-shaped ring means the center is positive when the plus sign points at the dot. Measure anyway. The two common hole sizes, 2.1 mm and 2.5 mm, almost fit each other and that is how the center pin gets bent.

Specification. The right-hand column is what is typical. The label on the part in your hand wins if they disagree.
What to look for	Usual figure
Ethernet	Often 24 AWG solid in the wall, stranded in patch leads. Four color pairs. Solid hates repeated flexing.
Magnet wire	From a dead motor or a transformer you are not keeping. The enamel is the insulation. Scrape it or it will not solder. It is not mains hookup.
Limits	Low voltage only, unless the insulation was originally mains-rated. When in doubt it is not.

Volts are electrical pressure, amps are how much current is flowing, and ohms are how hard the part resists that flow. A higher voltage than the part was built for is how salvage parts die on the bench. If a cell in the table says “read the stamp”, that stamp is the whole specification.

What people actually use it for

Signal wiring
Low-voltage power at the current the gauge allows
Twisted pairs for anything noisy

Leave this one when

The insulation is cracked. Old PVC does this and then shorts in the bundle.

Buying a new one is the better idea when

A spool of silicone hookup wire for anything you will flex. Salvage ethernet is for fixed wiring.

How to tell if this one still works

Continuity, then a nick inspection.

Tools you will want: Cutters, Iron.

Words on this page

Short meanings, so the rest of the entry is readable if you are not already doing this every weekend.

mains: Ordinary household wall power. It can kill. Unplug before you open anything that used it, and do not experiment on live wiring.
transformer: Two coils on an iron core. It changes voltage and, in a proper one, isolates the output from the wall. Heavy old adapters are this. Microwave oven transformers are a different, dangerous kind.
continuity: A meter mode that beeps when two points are connected. It is how you map a switch: beep, then click, then see if the beep changes.

Where people actually find it

5 notes, most useful first. “Leave it” means the part is in that machine and you should not take it: it is dangerous, worn out, or only useful if you already know that exact repair.

Harvest at a glance
From	Call	How many	How often	Where it sits
Desktop PC	Worth it	a harness	always	Supply cables.
Headphones	Bonus	1	always	The cable.
Fluorescent fixture	Bonus	a run	usually	The leads.
Seasonal light string	Bonus	metres	always	Between lamps.
CRT television or monitor	Leave it	the yoke	always	Around the neck.

Worth pullingDesktop PCa harness · always
In this particular machine
Color-coded 12 V, 5 V, and ground, already terminated.
Where to look
Supply cables.
How to get it out
Cut the connectors you will reuse and label them.
The condition to expect
Insulation is usually still good.
Bonus, if you are already in thereHeadphones1 · always
In this particular machine
Fine enameled strands. A repair nightmare, a decent short lead if it still beeps.
Where to look
The cable.
How to get it out
Test each conductor.
The condition to expect
One conductor open is the usual fault.
Bonus, if you are already in thereFluorescent fixturea run · usually
In this particular machine
Mains-rated, if it was mains-rated.
Where to look
The leads.
How to get it out
Do not downgrade it into a mystery bin.
The condition to expect
Good.
Bonus, if you are already in thereSeasonal light stringmetres · always
In this particular machine
Thin, often 28 AWG or finer.
Where to look
Between lamps.
How to get it out
Fine for signals. Not for current.
The condition to expect
Insulation cracks on old sets.
Leave it — present, not yours to reuseCRT television or monitorthe yoke · always
In this particular machine
A deflection yoke. It is not a benign coil to unscrew for copper.
Where to look
Around the neck.
How to get it out
Leave it.
The condition to expect
Leave it.