80 series transmission lock?

[Don Sutherland]

Cruiser won't go into gear, it's stuck in Park. I can pop the little cover and manually push the safety switch and have it go into gear. Here's how it happened:

• I was driving around delivering a bed with my small flat bed trailer. I unhooked the trailer while the Cruiser was on and in Park. When I got back in, it wouldn't go into gear.
• The only thing that changed was I wired in an amp/sub about 2 weeks prior to this problem.
• Everything else appears to work and no fuses appear to be blown.

I've tried some basic troubleshooting but before I tear into it, somebody has had to have seen this problem before. Thanks.

97 40th, factory F/R lockers. 225K miles.