I will be installing a Momo Club 4 Steering Wheel on my '88S4 and was going to do a photo How-to...when I remembered that I'd gotten the directions some time ago from Bill Ball's web site. It's so well written that I could never do as well. At any rate his link is still up and running but I didn't want to link to it without his permission.
Here's a link to Bill Ball's instructions for installing on a 928S4:
Hi. The Horn button comes off with a very stout yank while holding both ends
of it. It is flexible and will deform while you are yanking it. The real trick
is to use enough force to yank it off, but to have little or no follow-through.
The reason is that after the snaps that hold the horn button on release, it is
still held up by the wire connection for the horn itself.
That wire only allows about another 3 or 4 inch of travel before it comes to the end. If you are lucky, when you reach the end of the wire and are still yanking, you will simply pull the bayonet connection loose. Or, you might break the wire.
After that you will need a deep socket, or better yet, a socket with an extension to remove the nut holding the steering wheel on. You may find that it takes a lot of torque to break the nut loose, or you may find that it is just finger tight. I have found it at both extremes. Before you take the wheel off, be sure that it is lined up with the front wheels straight. If you have noticed that the wheel is slightly cocked when driving straight down the road, set the wheel at that angle before you remove it. Then when you put the new wheel back on, set it straight and you will have solved that little discrepancy.
Here's a good link:
While removing the pad, it helps to start at the left or right lower corner. there are 3 tabs holding it, lower left, right, and the center upper side.
The nut is a M18, 27mm socket. Be careful for the contacts below that feed the horn signal. These sliders sometimes bend or loose contact.
The M18 easily takes 93Nm torque, but this low profile nut it is not supposed to be that tight. I don't have a spec on that but I tighten it up as fast as I can while counter holding the wheel with the other hand. (and I'm not that strong... fuzzy , I know)
1992 Porsche 928 GTS Midnight blue