Switching & protectionRebuild shelfHand tools, works as-is

Automotive ISO relay

Also called Bosch relay, cube relay, 30 A relay.

The standard 12 V relay. Pin numbers are an industry habit: 85 and 86 are the coil, 30 is common, 87 is normally open, 87a is normally closed if it exists.

If you are new to this category

A switch opens or closes a circuit. Some switches are for your finger. Some open when they get too hot and stay open. Those do not reset. A relay is a switch that a small current turns on so it can control a larger current. Use the rating printed on the part.

Click it and listen. Then use a meter on continuity, which beeps when the contacts touch. Do not guess that a small switch can run a motor.

The three legs of a snap switch

Common is the moving contact. NO means normally open: that leg connects only while you press. NC means normally closed: that leg is connected until you press. Click the button while the meter is on continuity and write down which beep matches which leg.

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
Coil	12 V, about 60–90 Ω, roughly 150 mA. Some have a built-in diode or resistor; polarity matters on the diode versions.
Contacts	20, 30, or 40 A, printed. Inrush of a motor is higher than its running current.
Form	SPST (4 pin) or SPDT (5 pin)

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

Any 12 V load bigger than a logic pin
Headlight, fan, pump, solenoid
A junkyard will sell you five for the price of one new 'smart' relay

Leave this one when

The case is melted or the pins are loose. Relays that have been overloaded weld shut.

Buying a new one is the better idea when

Almost never, unless you need a sealed one with a suppressor and a datasheet for a production build.

How to tell if this one still works

12 V on 85/86. Click. Beep 30 to 87 only while the coil is powered, and 30 to 87a only when it is not.

Tools you will want: Meter, 12 V source.

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.

Where people actually find it

1 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
End-of-life car	Prize	several	always	Fuse and relay box.

Prize — take this firstEnd-of-life carseveral · always
In this particular machine
ISO cube, 12 V coil, 30 or 40 A. Pin numbers molded in the socket.
Where to look
Fuse and relay box.
How to get it out
They pull straight out.
The condition to expect
Good.