Is there any connection between the two systems on a 98 ml320? When the a/c is on, only one of the two horns sounds. With a/c off, horn blows normally.

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87 300e (white/black; amg body kit)
88 300ce (red/cream; amg body kit)
93 300ce cabrio (white/blue/blue top)
93 300ce cabrio (black/grey/black top)
98 ml 320 (totaled @ 137,000 miles)
99 clk320 (black/grey/black top)