New to forum with my first post.
My steering switches failed as well on my SST18. Turns out the switches themselves weren't bad, but the rubber boots had hardened. (Was also a problem I noted in cold weather prior to total failure.)
I trimmed the boot from the switch 2 years ago and it's been fine since. I don't mow in wet grass, so there isn't much chance of the switches getting wet (as the boots would be to protect). Seems to have solved the problem.
As a side note, the battery charging capability on my SST has given out. New battery, but still no charge. When voltage gets down to around 5, steering quits...first in reverse, then forward as well.
Would this be a simple replacement of the module on the right side of the engine, or something internal?