Those schematics on the sides of relays actually mean something! Who knew.

https://www.12voltplanet.co.uk/relay-guide.html

I was researching if my relay was surge protected for a circuit I'm planning, and lo and behold the diagram on the relay itself tells you.

If it happens to matter to you if the relay is resistor protected or fused or diode protected or not (for example, surge protected relays may not turn off as fast as non-protected relays, which might matter to you), then often you can see what you're working with simply by the diagram on the relay!

Cool!

On the link you can scroll down, or if you are lazy, see here:

Now you just need to learn the color code for the stripes on resistors, and you'll be all set.  

If you're like me and just have a stack of relays in a drawer, those diagrams are essential :)

stuart in mn said:

Now you just need to learn the color code for the stripes on resistors, and you'll be all set.  

Bad Boys R*ape Our Young Girls But Violet Gives Willingly (maybe not pc these days, but that's how I learned it long ago).

In reply to earlybroncoguy1 :

Bad Booze Rots Our Young Guts But Vodka Goes Well - Get Some Now

Includes the tolerance bands.

How about solving a story problem. I have an old Volvo which has 7" single headlights connected through a relay where when you pull the spring loaded lever back once, it switches from low to high beam and when you pull it back again, it switches from high beam back to low beam. I want the low beams to be always on no matter if the high beams are on or off.  That lever also flashes the headlights on even if the lights are turned off.

1972 Volvo 1800E Wiring Diagram

Two options:

1. Two separate relays. One triggers the low beams using the headlight switch. They're on whenever the switch is on.
   The second relay is a latching relay powered by the low beam power and triggered by the stalk. 
2. Connect the high beam power wire to the low beam power wire with a diode of appropriate fortitude, post relay. To make sure you don't overload the circuit, switch to LED headlights :)

In reply to Keith Tanner :

Thanks, I suppose it might be a good idea to switch to LED lights since running both low and high beams of the single element bulb at the same time might generate a lot of heat. Plus, having four 55 watt bulbs on at the same time might be tough on the Delco 12SI alternator I have plus two electric fans, fuel pump, and computer.

Relays are fun. You can do all kinds of fun tricky stuff with them. They are also FAR more simple than they are usually made out to be. Its just a light duty switch to control a "heavy duty"(usually 30 amps rating) switch. 
 

some will have a snubber diode between the pins for the light duty switch, 85 and 86 to stop flyback voltage from the coil. 

In reply to VolvoHeretic :

You'll definitely need to change the headlights to LED or a different setup to make that work.  Running both filaments in a dual filament headlight bulb will typically overheat and kill the bulb.  Plus, depending on the lights, it may not give a terribly useful beam pattern anyway (often has too much light up close and kills your distance vision). 

Keith Tanner said:

If you're like me and just have a stack of relays in a drawer, those diagrams are essential :)

Maybe not a big stack, but yes:

Price list for my favorite yard.

RELAY 6 OR MORE$9.89

Yep you can get as many as you want for $9.89. Bring a bag with you.

In reply to rslifkin :

Thanks, after posting last night, I started looking up E-code European headlights like I used to have back in the 70's and understand what you are talking about. I want to light up the right ditch so that I can watch the deer jump out right before I hit them at 75 mph on the interstate. I think that I will just get a third bolt-on light aimed into the ditch and take my chances with the cops. 

If there are cops available to see your high beams in action, you shouldn't be running your high beams anyhow because you'd be blinding them. 

You can install E-codes in your Volvo now and get that nice cutoff with the right kickup and no wiring changes.

rslifkin said:

In reply to VolvoHeretic :

You'll definitely need to change the headlights to LED or a different setup to make that work.  Running both filaments in a dual filament headlight bulb will typically overheat and kill the bulb.  Plus, depending on the lights, it may not give a terribly useful beam pattern anyway (often has too much light up close and kills your distance vision). 

There's also the issue of the ground side of the lights not being sized to carry the current from both filaments at the same time.