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Relay Coil has Polarity?

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Follow the indicated polarity, and you won't go wrong. In many cases, the relay may possibly include a diode, and when you order one, you might get that version. If you follow the markings, it won't make any difference.

I recently learned that automotive relays come in a common package, but some relays in that package include a diode and others do not, which is not necessarily marked on the package. Follow the convention and it doesn't matter.
 
Sometimes it's not the relay that has the diode, but the socket: https://ceautoelectricsupply.com/product/5-wire-relay-socket-with-diode-protection/

The automotive relay https://www.12voltplanet.co.uk/relay-guide.html
Screenshot_2021-06-23 Automotive Relay Guide 12 Volt Planet.png


In today's world, there is a lot of "don't care" stuff going on, but "sometimes it matters.

In the automotive relay, we have the diode problem, the polarity markings that most ignore, the diode in the socket instead of the relay and the terminal numbers being different.

What's a little disagreement between friends?

I do remember when I was in an explorer's post at HP, I was asked what color wire (black, white_ would have the fuse and switch?
I said black and the guy teaching us was wrong. This was a US 120V black, white, green system of colors.

An AT&T telephone repair person who said he taught how to repair the telephone lines. I asked him why handset to station lines are reversed. He said it didn't matter. I finally came up with a good reason: It keeps TIP and RING the same colors except through the wall cord. Patch cords would be straight-thru.

The word of thermocouples threw me. red, most of the time is negative.

Sorry, screenshot doesn' t work right.
 
Don't mean to best this to death but....;)

If your circuit doesn't require a polarity sensitive relay, then for part interchangeability reasons, its better not to use one.
 
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