99 suburban shutdown w/brake or lights applied

1999 chev suburban 1500 4wd intermittently will turn engine off when brake is applied to put it in gear or stopping while driving.some times it will restart and some times it will take several times turning key off and retrying.when this is occuring you can not touch brake or turn on headlights.there seems to be no particular circumstance for this to happen and it will straighten out just as suddenly as it occurs.this has happened to me at 70 mph trailering a boat on the interstate when there was a slight dip in the road which caused a bounce but then on the same trip minutes later there was rough pavement in a construction zone and it kept running.this can appear after vehicle has been parked and was fine at the time it was parked.:confused:

I would guess the ignition switch is the problem.

I came across a Ford F-350 that would shut down when put in reverse.It turned out to be a broken ground wire.Fortunatly it was easy to find.It did it all the time.Does your suburban have the security system?This could be getting activated.
chuck's