Everything you wanted to know about RELAYS...

[WagonCrazy]

I have now wired up 2 old cars pretty much from scratch, and fumbled my way around wiring systems on other vehicles. i self learned alot about how the power moves thru circuits (and when it doesn't move thru them as intended).

I found this article recently, and it contains some simple truths about how automotive relays work. You guys might find it helpful too...
https://www.hagerty.com/media/opinio...2871acb8db3597

[NickP]

Thanks for sharing

[chevynut]

There is one thing to watch out for and he eluded to it. Generally, you can swap terminals 85 and 86 but some relays have diodes in them to protect the driving circuitry. If you wire it backwards, the diode will conduct and the relay won't operate. If you always make 86 the positive side, you'll be ok. He talked about terminals 30 and 87 and that they might have diodes on them, but I've never seen one like that.

[WagonCrazy]

Laszlo,
I'm circling back to your comment:

Generally, you can swap terminals 85 and 86 but some relays have diodes in them to protect the driving circuitry. If you wire it backwards, the diode will conduct and the relay won't operate. If you always make 86 the positive side, you'll be ok.

Take a look at this dual fan wiring diagram posted on Griffin Radiators website.

The 12v side is the orange wire-pin 85, and the ground side is the grey wire-pin 86. So do they have this backwards from what you are suggesting?(regarding diode's in the circuit)?

Screen Shot 2024-03-27 at 11.47.32 AM.png

[chevynut]

The 12v side is the orange wire-pin 85, and the ground side is the grey wire-pin 86. So do they have this backwards from what you are suggesting?(regarding diode's in the circuit)?

Yes, it's backwards from conventional wiring procedures where 86 is positive. However, as long as the relay doesn't have a diode in the coil circuit between terminals 85 and 86 it will work fine. Some relays do and some don't. Like I said if you always wire 86 to + you should never have a problem.

https://www.hagerty.com/media/mainte...relays-part-3/

https://www.youtube.com/watch?v=7nrDeQRTCm8

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

[WagonCrazy]

Got it. Wanting to know what the correct methodology is and you've covered that.

So a 12v relay with a diode would probably have a marking on it like this symbol?
Relay with diode.jpg

[chevynut]

So a 12v relay with a diode would probably have a marking on it like this symbol?

Exactly. The arrow on the diode shows the direction that the current will freely travel. It won't travel in the other direction. It's like a "check valve".

[567chevys]

Good information ,

This is a Site I used when I was younger it hasn't been updated in a long time but basis good information

http://www.madelectrical.com/electrical-tech.shtml