Hello to you all have the problem with my tacho unit at volvo 850, and indeed falls off and to the tacho would be the ride out. by knocking on the amature board the tacho goes again, but the annoying now I have got a tacho unit needed and this then built in and wanted to know if also everything goes there the tacho goes without knocking is only strange when I drive faster than 60 km also this tacho falls off and the tacho lighting does not work even if I reinstall the old one goes all again until I just have to knock again it can be the one that the used tacho has other cable laying like tacho signal ?? must the used one the baugliech is the same nr have so that he goes overhaubt??? had also narrow a tacho unit from v 7o 1 in it goes also everything except tacho since not what must I pay attention so that the used tacho goes because of the cable laying ? thank you in advance and thank you for every 850 b14 7