Radio & windows die when in gear

I have a 1996 MercurySable that loses radio volume (screen still shows it's on), power windows, & interval wipers (but not full-time wipers), plus some power steering when in reverse or drive. Everything's normal in park or reverse. It started as intermittent radio volume loss only when in drive or reverse, then progressed to all the above all the time when in drive or reverse. I looked at forums that referred me to a TSB directing me to change the neutral safety switch, which I did. Problem still there, no codes. Any ideas?