Late to the party - but there's a very long 17 page thread over at the R170 forum. Other may end up here and go there.

I personally spent a lot of time with these about 6 years ago....on my SLK230...same pump as my SLK32 (=crossfire SRT6 in mercedes clothing - or the other way 'round)
I ended up buying a new pump back then. Then when I got the SLK32, I actually took my new 1999 SLK230 pump out and put it in my SLK32 and vice versa.

This 17 pager post indicates the interior light timer is tied in with the PSE (Pneumatic...something something...)
here

Lots of info for others...but glad to hear you got it fixed.

b22b