12 volt relays, how they work

[roadman5312]

     Just thought I would throw this out to help anybody that needs this info.  I've worked on to many cars where somebody tried to run a cooling fan or fuel pump off a toggle switch and burned stuff up. E body headlights come to mind   .  Ok, so think of a relay as a heavy duty switch that transfers direct battery power to the accessory ( fan, pump, etc ) that is triggered by the toggle switch, thus taking the load off the toggle switch. Heres how it works. First you have direct battery current going into terminal 30. Terminal 85 is grounded. Now you hook up your toggle switch to send 12 Volts to terminal 86. This can come from accessory wires or always positive sources. Now when you flip the switch terminal 86 goes thru a coil and grounding thru terminal 85, closing a set of points that connects terminal 30( full battery voltage ) to terminal 87 out to your fan, pump, etc. So there is only the load on the toggle switch of closing a set of points. Solves lots of problems. Hope it helps.      BTW, you can also reverse triggering by connecting 30 to 86, and sending the trigger from the toggle thru a ground.

[73440]

thanks, that must be the standard relay, I recognize the terminal numbers,
any idea why the particular numbers are used ?

[73440]

think I answered my question.
looks like DIN 72552 explains it.

[1 Wild R/T]

thanks, that must be the standard relay, I recognize the terminal numbers,
any idea why the particular numbers are used ?

https://en.wikipedia.org/wiki/DIN_72552

If you ever look at a European vehicle wiring schematic they use the DIN standard numbers on practically every component...  If you look at allot of the switches, motors & other components every terminal is numbered... Those numbers directly relate to the DIN standard...

[73440]

Thanks, knowing the numbers and their meaning then should help tracing electrical

[dodj]

Thanks, knowing the numbers and their meaning then should help tracing electrical

When a standard is used it really helps. Trouble is, with a lot of equipment various manufacturers,they like to go with 'their own' numbering systems and makes it difficult for someone without their training or manuals.

[Katfish]

Nice info, never hurts to cover the basics.

[MOPAR FANATIC]

  IF this is just the basics,Man am i in for it when i have a wiring problem 
last year while driving my dailey driver i could smell something electrical burning,just got it in my driveway,flew open the hood and smoke was pouring out.coarse it stalled out at that point.i could'nt figur it out after checking fuses and relays on my,NOT knowing sqaut about electrical i had it towed to a shop.$450.00 LATER it was fixed,had a bunch of blown fuses and relays.plus they reset the pcm and the car has never run so good since i got it.plus check engine light  has never come on since then.anything eletrical goes down to my buddys shop from now on. 

[ShelbyDogg]

If you do fuel injection or have any other computer stuff on board. I always use a diode across the coil to kill the flyback spike that surges through your wires when the relay turns off.  Think of that relay as a little coil with the switch acting like points opening. You can probably feel the shock if you held the terminals.

Any small diode will work. If you hook it up backwards, it will blow like a fuse and leave you unprotected. Remember, electrons flow Negative to Positive so the point and line have to be towards the + side.

[blown motor]

Thanks Mark. I'm almost wiser now    Electrical just confuses me.