Car is a 1975 and I am going back to the OEM steering wheel from a Momo. I bought a steering wheel listed for a 1975 car, but it didn't come with the horn pin. I see there are two types, long and short with each saying they fit a 1975 1.8 car. How do I know which is correct for the steering wheel I have?

Short.
https://www.ebay.com/itm/284708651730?fits=...ABk9SR-zDgevVYQ

Long.
https://www.ebay.com/itm/284771763445?fits=...ABk9SR-zDgevVYQ

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914-6 takes the longer 44mm. Don’t know about the various 914-4 steering wheels.

Not in a ‘75

Right. 72-76 uses the later plastic hub with the plastic turn signal cancel disk and a brown wire that connects to a tab on the horn pad.
Early wheels 70-71 use a long horn pin. 914-6 uses a short pin since there is no plastic hub to space out the wheel.

@mepstein Can you clarify, so the 72 to 76 914-4s don't need a pin at all, since the brown wire takes care of that function? In the PET for those years there is no pin shown at all, so that would make sense.
Thanks in advance for the education.

As mepstein said the difference is the slip ring.

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#4 is the slip ring, it replaces the pin. The brown wire (ground) connects to the batwing which completes the circuit to ground when the batwing contacts the slip ring.
The horn has power all the time, when the circuit is complete to ground the horn operates.

Yes. The 70-71 has a plastic hub with a metal tab to cancel the turn signal. The 72-76 has a plastic hub that accepts the plastic horn cancel ring with the brown wire for the horn. No pin.

@mgphoto and @mepstein
Thanks so much, that really clears things up for me.

Seems I don't have the brown wire I assume I need for the OEM horn to work.

This is my working Momo set-up and I understand how the bronze ring is in constant contact with the contacts of the directional mechanism and how when the horn button is pushed the horn grounds out and sounds.

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And the OEM wheel I picked up. Do I need to connect a ground to the spade connector? Am I missing something? I don't see where the stock wheel would make contact with the directional contacts to receive power. I am also missing 4 small screws that connects the back plastic hub to the wheel.

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Is the missing piece #4?

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Seems like I answered my own question by looking at other used steering wheels on eBay. #4 on the steering wheel I bought had been removed, probably to sell separately.

I found one on Ebay and grabbed it.

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Do you have the plastic steering wheel adapter?