Have 2000 ML430 and the horn won't work. Have checked and both horns are connected, fuse is good and have swapped relay with a known good relay and horn still doesn't work. Recently had the truck in the shop and had the mass air meter replaced and also had the engine mounts replaced. Could the shop have done something in either of these to disable or disconnect the horn? Any ideas would be appreciated.

IF the horn relay is jumped (connect 30 to 87) do the horns operate?

IS fuse 37 good?

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MERCEDES Benz Master Guild Technician (6 TIMES)
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190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
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Fuse 37 is good.

What are pins 30 and 87? The pins on the relay are #'s 1, 2,3 and 5.

I have taken one of the relay's with the same part number that I know is good (one of the turn signals) and swapped it with the horn relay and still get nothing from the horn.