I added a tach to my 240D a few weeks ago just like what was posted in this thread:

DIY tach for 240D w EGR- easy!

My question is why would my tach peg when the horn is honked? I just noticed this last week as a rarely use my horn. I know my grounds are good, i cleaned and tigthened all of those when i bought the car. I can't pin this one down. Other things like the compressor switch (temp dial) etc will make the tach jump just once in a while very briefly like 100-200rpm worth. The horn however will peg the tach if you hold it down. Anyone have any ideas?

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