I had a similar problem on my 190E. The SRS light would come on intermittantly while driving straight ahead, wiggle the steering wheel and the light would go out. I had to pull my steering wheel to access my Ignition switch so I examined the horn and SRS contacts. The copper contact rings in the steering wheel were worn concave and the brushes were also worn. there was a large amount of black dust material around the contacts. I cleaned the contact rings with electrical contact cleaner [DeOxit]and a pencil eraser and also cleaned the contact brushed for the horn and SRS system. I used compressed air to remove all the dust material and reassembled. so far so good the only time I see the SRS light is on prove out and my horn also seems to be louder.

FYI, My steering wheel bolt was on extremely tight from the factory, a 1/2 inch air gun would not remove it until I took a small torch [real small] and heated the bolt thoughly, then the bolt could be remove with the impact gun. M/B used red locktite on the steering wheel bolt. I used a very small amount of blue loctite on the cleaned bolt during reassembly.