[Bill, here’s now my best attempt at a response]

The horn contact ring in the steering wheel is part of the clockspring assembly mounted at the top of the steering column with a spring loaded, metal tipped contact button imbedded in the steering wheel. Access to the horn ring and clockspring will require disabling the SRS system and removal of the steering wheel.

I had submitted a complete feature article for the FAQ here on the clockspring some years ago, including pictures, but I can no longer find it. It may have been removed during the last major edit done some years ago. I will include excerpts here.

STANDARD DISCLAIMER: Any work involving the SRS system is done entirely at your own risk. The brickboard and its contributors assume no liability, including failing to provide accurate or complete information or you not being able to follow instructions. Seek the services of a qualified technician if you do not understand or are not confident working around SRS components.

Disable the SRS system by disconnecting the battery negative terminal and safely bagging it out of the way. A two minute discharge is considered adequate.

Start by peeling back the airbag cover for access, starting across the top -don't stretch it any more than you have to, doing it in warmer shop conditions is a good idea. Remove and disconnect the airbag (two torx screws and connector). When disconnecting the airbag wires or handling them, avoid touching the bare contacts and avoid any stray electricity or static discharge.

Removal of the steering wheel of course requires removal of the steering column nut. You will need a breaker bar and short extension. You will likely not be able to restrain the steering wheel by hand. Tie a rope through the crossbar and around the upper door frame, slamming the door shut on the rope before tightening the rope knot. Leave the window fully open for access. You should now be able to loosen and remove the lock nut.

BTW, if the horn button switches need to removed, there are tips in the FAQ. Much of the rest of the information there is for pre-airbag days.

Prior to removal of the steering wheel, you need to secure the clockspring from unwinding. You do this by advancing the lock screw in between the plastic locking tabs. During steering wheel removal, do not turn the steering wheel which will risk breaking the plastic lock tabs. Note the precise orientation on the steering column splines with a felt pen and scribe before you begin. For re-installation, best to use a torque wrench, again using the rope, 44 ft-lbs is the spec I see in an aftermarket manual. Do not forget to back off the lock screw when you are done.

Although a puller is often suggested for use with steering wheels, you shouldn’t need to do this. Pound firmly with your fists behind the steering rim at the cross yoke. Pound both together and alternating. Within about six good pounds it should start to loosen and can be wiggled off the splines.

You will now have access to the horn contact ring and the horn contact button. If you're lucky, the contact ring and/or button contact may just need a good cleaning. A wipe of dielectric silicone grease can be used as a lubricant and as I recall is recommended, but can also attract dust and dirt. If the button is worn out or one of the wires is broken that connect to the horn button switches then the part is still available as p/n 1387738 from Volvo and through resellers like ipd https://www.ipdusa.com/products/22469/Horn-Slip-Contact-740-760-780-940-Genuine-Volvo-1387738-140699

Failing that, there may be a problem with the horn ring being worn out or the wiring to the clockspring somehow having failed or the clockspring itself having cracked or been damaged. You will then want to remove the clockspring to use a meter to verify continuity. Just make sure the locking screw remains in place, otherwise the clockspring may unwind and will now need centering (please re-post if this happens for further advice). If not centred correctly and the alignment with the steering column preserved then the clockspring may soon break from strain when reaching end of travel at the steering end locks. With the clockspring not in place, you must not turn and loose track of the steering column or wheel position such as to lose rotational alignment when the clockspring was removed. BTW, if this happens and the clockspring breaks, as once happened with me when an idiot body shop tech put a steering wheel back on incorrectly, best to seek a used clockspring from a low mileage wreck rather than new as they ain’t cheap.

Good luck.

As a tip here while I’m mentioning this. Some 900s develop an annoying squeak at the top of the steering column. If you ever remove the clockspring, you could take that opportunity to grease it. It's a bit fussy to do, as follows. There’s a tapered white plastic spacer ring on the steering shaft visible behind the clockspring. It’s held in place by a circlip sitting in a slot. Note that the spacer ring is supposed to have a split in it -so don’t get excited. The spacer ring sits at the top of the steering shaft upper bearing. There’s a corresponding steel metal spacer ring that you can’t see on the under side of the upper bearing. You can push a little grease around the spacer ring if you want, just don’t remove that circlip or remove the plastic spacer unless you’re prepared for an adventure –they can be difficult to get back on and may necessitate removal of the entire upper steering column. I'll mention here for others who may read this, on some 700’s (not 900s) the metal spacer may be on top and the plastic one on the bottom. In those cars, if the steering column has developed a clicking sound then upgrading to the new style of spacers is one possible cure, but both rings must be replaced and the upper steering column will need to be removed (non-trivial). There’s a technical bulletin (TP 30801 dated Jun-89) fully describing this upgrade.

Again, good luck.
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Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now