A few days after driving through heavy rain and snow, my merc suddenly wouldn't start. When I put the key in the ignition the dash lights came on and there was a clicking sound. Garage merc techs told me I would have to either replace the ignition switch or steering lock mechanism (at a huge expense!). I suspected a moisture problem so managed to remove the cover under the steering column. Traced the clicking sound to the steering lock mechanism. Managed to unplug it.( not easy to reach!) sprayed q20 onto contacts.dried it off. Plugged it in again. Car starts again. Seems to be starting fine now. Saved myself a lot of money! Hope this helps anyone with a similar problem.