85 W123 Ignition Switch & Tach

[rmmagow]

Hi All,
Car starts and runs OK, ignition switch seems a little loose but I've not had issues with it. The question, can a faulty ignition switch affect the operation of the tach in an 85? I know the 85 has an odd-ball tach setup and I am inclined to think I need to replace the RPM sensor in the bellhousing but if the switch could have an effect I'd like to have a look-see there too.

I've checked the OVP thing. Disconnecting the RPM sensor and testing at the male ends I get a resistance reading with the engine off but no voltage reading with the engine running.

Funny thing is sometimes when switching the car off the tach needle will jump a little bit. Fiddling with the switch while driving doesn't cause the tach to respond in any way.

Thanks

[andrewjtx]

You might check the ground connection for the cluster as well. I don't think the ing switch would have much to do with it, though. It wouldn't hurt to make sure all of the switch plug wires are snugly seated...