I can generally do my own Volvo work (2-850s, 1-xc, 1-240) ie timing belts,brakes, etc. My 850 sedan needs an inspection --but the horn has been working with diminished reliability. As my daughter needs the car out of town "yesterday" and I wasn't able to diagnose the issue rapidly--I opted for the "quick" rube repair job -for safety and inspection purposes.
I am aware the wipers and horn are on the same circuit--and decided to install a push button for the horn.
I snipped the small and larger blk/yellow wires near each horn -spliced a positive lead from the battery to both larger wires (3 wires together) --and connected a "new" ground wire to both smaller wires (3 wires together). Then I spliced in the push button wires-(along with a 15 amp fuse) to my new pos. wire coming off the battery. Ah --yet another successful country rube repair job as the handy dash push button works great!!
Alas --to my chagrin--the wife returned from her trip to work this a.m. as the wipers no longer work. I've tried different combos with splicing the horn wires together thus far to no avail.
I'm hoping someone can nudge me in the right direction here --and save me
an unknown # of diagnosing hrs. Multiple thanks in advance----
woops -forgot to mention that I have tried connecting cut hanging wires ie two small ones & two larger ones together in attempt to remedy the wiper issue (didn't work).
FORGET IT---EVERYTHING is OK---I'd checked fuse # 34--but missed that it was blown!---wipers are working--and so is the horn-job!

 

Well if you had not found the issue I would have recommended putting everything back to OEM then get the IPD horn repair kit. I did not know these repair kits existed when by horn died several years ago on another 850. I found all the parts I needed to fix the horn connections/isolation/etc from Ace Hardware.