The horns on my w123 on occasion tend to fill up with dirty water and they stop working. I shook out most of the water and got it to make a faint beeping sound. After about five minutes in a toaster over (until steam stopped coming out) I took it out, let it cool, and it worked once more.

A fine horn from a luxury car at a junkyard cannot cost more than $5.00. A new horn at any autoparts store costs about $15.00.

12v is 12v. A relay should not make any difference.

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Semibodacious Transmogrifications a Specialty

1990 300D 2.5 Turbo sedan 171K (Rudolf)
1985 300D Turbo TD Wagon 219K (Remuda)

"Time flies like and arrow, yet fruit flies like a banana"
---Marx (Groucho)