Starter staying on when in neutral...

Over the last couple of days, my hmmwv has started to have the starter continue running while in neutral. It's an 86 model with a 6.2. Once I shift into drive, it seems to stop and everything runs fine but when you shift into neutral to shut it off, you can hear the starter engaging. Or at least that's what it sounds like to me.
I've been shutting it off in gear and parking it in gear to keep this from happening while it is not in use.
What should I be checking first? Is there a regular starter solenoid that may be bad or some other sort of controller?
I've worked on plenty of jeeps and trucks but never a diesel, for whatever that's worth...

Unless your ignition switch is fried or the PCB is fried, you have a short circuit.

Easiest thing is to check ignition switch first.

Also check the starter. The Bendix drive can go over-center if the pinion retainer is broke or missing. This makes the contactor stay connected. Happened to mine, also a 1986 6.2 with only 9000 miles on the odometer. Verified miles too so it wasn't a rebuilt starter. I am thinking the parts shattered, possibly from incorrect heat treatment. You need to drop the starter to check.

Mine was so far gone it had broke the nose cone.

You running an aftermarket key switch by chance? I had to replace mine for the same issue.

Mark

I will put a meter on the ignition switch. It is a cheap aftermarket one with a tiny little key. Same switch worked well on a cj5 but probably too small for this truck. I wasn't the one who installed it.