Starter cranks in ON position and continues to crank after engine starts.

Ignition system problem on my 93 M998, 6.2, 3 speed.
When turning ignition switch from OFF to ON, starter will occasionally engage, WAIT light does not come on. Usually, if I switch back to OFF the starter will stop. However, sometimes it continues to crank in OFF position without engine starting.
On other occasions, the switch works as it should.
Sometimes after moving from OFF to ON the WAIT light comes on for the proper amount of time, light goes off, I turn switch from ON to START, starter engages, engine starts, but starter does not disengage. I then move switch to OFF but starter continues to crank. After several ON to OFF tries it stops.

I pulled the switch and tested continuity between the three post. In OFF position there is no continuity. In ON position there is continuity between two post. In START position there is continuity between all post.

Outside of switch is very clean. Handle moves as it should between positions. Spring returns handle to center as it should. There is no roughness or sticking feeling when turning.

Since the starter engages when the switch is moved to the on position I'm wondering if the start box has any affect on the solenoid.

I had the same thing happening with a keyed ignition switch. Cheap, wore out.

Might want to pick up a new ignition switch to make sure it's not the cheaper item first.

This also might be a bad starter solenoid. When the solenoid is engaged electrically the electromagnet keeps it engaged with the ring gear but a spring retracts it. If it is rusty or the spring is broken it will not retract and run on with the ring gear.

What papakb said is likely spot-on, thanks to the very erratic behavior you get, but it will only cost you some time to do the following tests to be sure.

Here's a quick way to test for the solenoid failure: Ensure your vehicle is secured from rolling and your transmission is in neutral. Feel free to disconnect wire 54A on top of the injection pump if you want to be certain that your HMMWV won't inadvertently start. Open the cover for your DCA port, locate pin s and t. Using an insulated jumper wire, jump pin s to pin t...this will bypass the starter switch and EESS/S3 control box and cause the solenoid to engage and spin the starter. You can test this a couple times. If it seems to be producing those runaway start conditions, it's almost certainly the solenoid.

If that didn't work, the next test I would do would be to disconnect the start switch and again use your jumper to simulate the switch being in the run position and further to the start position. If you have the runaway start conditions through this test, it's [sadly] almost certainly the EESS/S3. If the condition is now gone, it's thankfully the cheap-to-replace switch.

The variable through all of this is bad wiring. Poor connections or damaged wires can make all kinds of unintended black magic happen. That can only be tested through careful inspection of the wires and their connections. Some won't show very easy as the breakage/corrosion may be inside a wire jacket, where you can't see it.

Working it out...

Maybe the off-run-start switch. Not likely biased on on your tests and a starter hang / run.

Off-run-start switch, signals control / lockout circuits in in the BOX. More to it than simple old school switch to function. More like the five hundred dollar toilet seats.

OFF is off. Engine and accessories, Lighting circuits not involved. Still power in the box.

RUN drives a control relay to power all circuits such as IP, cold start, fan clutch system, heater fan, wipers. Lighting circuits not involved.

START is a little tricky as it goes thru the box and requires neutral safety switch to engage starter. Box detects engine running (idle) from alternator AC output sense to lock-out starter or re-engagement.

My two cents worth. IF and that's a big IF, everything is working correctly as stated... 1. engine is running, 2. alternator sense lead output is correct, 3. starter should have disengaged and should not allow a start if engine is running.

That said, Box is wack or maybe ?? starter solenoid could be hanging up??. Wire Fox test would clear up any funky stater sticking. Nobody said "ground kit it" yet

Could be easy fix with 300 dollar hammer or new box,

CAMO

Thanks for all of the help.

I'm pretty sure, as has been suggested, that the control box is the problem. I've tested the switch extensively and it is working as it should. Grounds and grounding kit are good. Starter and starter solenoid tested good.

The bendix is not hanging. The starter engages as I'm turning the switch to "ON" and remains running for 10 seconds or more regardless of switch position. If the starter does not come on until I switch to "START", the engine starts immediately but the starter motor continues to run for another several seconds even if I switch to "OFF".

I disconnected the batteries, then removed and opened the Nartron box, everything looks almost as new. No signs of water having ever been in the box, bare metal is bright and shinny. All components are covered with waterproofing rubber material. There are 2 larger 12 volt relays and 1 smaller 12 volt relay. The control board and it's components are encased in black epoxy so nothing can be seen. I removed the rubber from the terminals on all 3 relays and energized the coils. Tested the contacts with an ohm meter. All 3 relays work as they should. They make and break immediately with no hanging and contacts ohm out good.

I'm beginning to believe its a component on the board but with the epoxy I cannot go any farther with it.