Sound, light, heatRebuild shelfHand tools, works as-is

Indicator LED

Also called 3mm LED, 5mm LED, panel LED.

The ordinary indicator. Through-hole LEDs from old boards are worth a jar. SMD 0603s are not, unless you enjoy tweezers. Polarity matters and there is always a series resistor in any honest circuit.

If you are new to this category

Speakers, lamps, heaters, and displays. To test a speaker, touch a 1.5 V cell to the terminals for a moment. The cone should click once. A heater can start a fire if you remove the part that was supposed to shut it off.

Heat and bright light usually mean household voltage. Unplug first. If the original safety part is open, find out why before you replace it.

The one-second speaker test

Touch a 1.5 volt cell to the two terminals for a moment only. A good cone clicks and moves. A scrape means the coil is rubbing, which will sound bad even if it still makes noise. The ohms printed on the magnet, often 4, 6, or 8, tell you what amplifier it expects.

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
Drop	About 1.8–2.2 V red, 3.0–3.4 V white and blue. Infrared is about 1.2 V and invisible.
Current	5–15 mA for an indicator. A GPIO through 330 Ω at 5 V is the usual habit.

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

Status lamps
A quick polarity and presence check

Leave this one when

The lead is a 2 mm stub you will never solder. Move on.

Buying a new one is the better idea when

A mixed bag of new LEDs. Salvage is for unusual shapes and panel mounts.

How to tell if this one still works

Diode test. The meter’s diode mode often lights a red or green LED faintly.

Tools you will want: Meter, Resistor.

Words on this page

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

polarity: Which side is plus and which is minus. Reversed polarity ruins a lot of electronics. The symbol on a power brick is the map.
series: Connected in a chain. Cells in series add their voltages. LEDs in series all go dark if one of them opens.
GPIO: A logic pin on a small computer board, such as an Arduino or a Pi. It can light an LED. It cannot run a motor or a heater by itself.

Where people actually find it

12 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
Solar garden light	Prize	1	always	The head.
Seasonal light string	Worth it	dozens	usually	The string.
Optical mouse	Bonus	1	usually	Optical illuminator.
Router or modem	Bonus	several	always	Front panel.
Electric kettle	Bonus	1	usually	Indicator.
Refrigerator	Bonus	1	usually	The lamp.
Clock radio or stereo	Bonus	several	usually	Display.
Cordless drill	Bonus	1	usually	The work light.
End-of-life car	Bonus	several	usually	Later cars.
Garage door opener	Bonus	1	usually	The courtesy lamp.
Motorized toy	Bonus	several	usually	Eyes and buttons.
Alarm clock	Bonus	several	usually	LED-display models.

Prize — take this firstSolar garden light1 · always
In this particular machine
A white LED.
Where to look
The head.
How to get it out
Note the polarity.
The condition to expect
Good.
Worth pullingSeasonal light stringdozens · usually
In this particular machine
Series LEDs. You cannot power one from 12 V just because the string said 12 V somewhere.
Where to look
The string.
How to get it out
Cut a dark section out only after the string is unplugged, and know the rest of the series math.
The condition to expect
One open LED per dead section.
Bonus, if you are already in thereOptical mouse1 · usually
In this particular machine
Often an IR or red LED aimed at the desk. Not a laser you can use.
Where to look
Optical illuminator.
How to get it out
Leave it unless you want the LED.
The condition to expect
Fine.
Bonus, if you are already in thereRouter or modemseveral · always
In this particular machine
Ordinary indicators on a harness.
Where to look
Front panel.
How to get it out
Keep the light-pipe with them if you want the look.
The condition to expect
Good.
Bonus, if you are already in thereElectric kettle1 · usually
In this particular machine
With a dropping resistor, sometimes a neon on mains.
Where to look
Indicator.
How to get it out
A neon is not an LED and will not run on 5 V.
The condition to expect
Good.
Bonus, if you are already in thereRefrigerator1 · usually
In this particular machine
Or a mains incandescent appliance bulb, which is not a general LED.
Where to look
The lamp.
How to get it out
Read the base.
The condition to expect
Good.
Bonus, if you are already in thereClock radio or stereoseveral · usually
In this particular machine
Or a VFD.
Where to look
Display.
How to get it out
LEDs are easy. VFDs are not.
The condition to expect
Good.
Bonus, if you are already in thereCordless drill1 · usually
In this particular machine
A white LED.
Where to look
The work light.
How to get it out
With its resistor.
The condition to expect
Good.
Bonus, if you are already in thereEnd-of-life carseveral · usually
In this particular machine
Or wedge bulbs, which are not LEDs but are still lamps.
Where to look
Later cars.
How to get it out
Note the base.
The condition to expect
Good.
Bonus, if you are already in thereGarage door opener1 · usually
In this particular machine
An appliance bulb.
Where to look
The courtesy lamp.
How to get it out
Not a special part.
The condition to expect
Good.
Bonus, if you are already in thereMotorized toyseveral · usually
In this particular machine
Ordinary LEDs.
Where to look
Eyes and buttons.
How to get it out
Note the resistor.
The condition to expect
Good.
Bonus, if you are already in thereAlarm clockseveral · usually
In this particular machine
Multiplexed digits.
Where to look
LED-display models.
How to get it out
The digit board is the usable unit.
The condition to expect
Good.