You may be correct that it is connected to the PTO. I tend to pick a point somewhere in the middle to check, so I don't focus on the one area that may lead me astray. If a quick inspection doesn't show a damaged harness etc, I would see what the engine is missing to run. Does it have spark at the spark plug? Am I assuming correctly that this is a Kohler w/ battery ignition? (has a cylindrical ignition coil w/ 2 poles and plus the plug wire?) If not disregard the below. If so, it needs 12v to the + side of the coil. If it does, then you are looking at something engine related. If it doesn't- the next thing I would check is chassis related.

I'm not familiar with the machine, but-
"When the problem started, engaging the PTO resulted in one of the lifter arms popping off. That's when I couldn't get it restarted."

IF this DOESN'T have an electric PTO, I'd suspect the deck attachment switch was knocked out of adjustment.

Thank you both for responding.

Tomplum, what is a "harness"? And how do I check? Didn't get a chance to see if it had spark or not, maybe can check tonite.

Bill kapaun, how do I check deck attachment switch. What am I looking for

This is a very old Deere but only 420 hours on it. We use it for light mowing when the ground us wet here (SW fla). Usually only in summer, otherwise use an X-Mark. Here's some info on the Deere

John Deere 112L
1985 - 1985���100 Lawn Series
Lawn tractor
Previous model: John Deere 111H
Larger: John Deere 116
Smaller: John Deere 111H

Overview
� Engine
Transmission
Dimensions
Photos
Attachments

�
Production:
Manufacturer: John Deere
Original price (USD): $2,690 (1985)
� John Deere 112L Engine:
���Kawasaki 460cc 1-cyl gasoline
full engine details ...
� Capacity:
Fuel: 2.5 gal [9.5 L]
� Dimensions & Tires:
Weight: 470 lbs [213 kg]
Front tire: 15x6.00-6
Rear tire: 18x8.50-8
full dimensions and tires ...
� John Deere 112L attachments:
�38" mid-mount mower deck
all 112L attachments ...
� 112L Serial Numbers:
1985: 315001
Final: 360000

how to read serial numbers...

�
John Deere 112L Power:
Engine: 12.5 hp [9.3 kW]

� Mechanical:
Chassis: 4x2 2WD
Cab: Open operator station.
� Electrical:
Ground: negative
� Battery:
Number: 1
Volts: 12
� Page information:
Last update: July 1, 2012
Copyright: Copyright 2012 TractorData LLC
Contact: Peter@TractorData.com

� gasoline
� 1-cylinder
� air-cooled
Displacement: 460 cc [28.07ci ]
Bore/Stroke: 3.5x2.9 inches [89 x 74 mm]
Power: 12.5 hp [9.3 kW]
Starter: electric
Starter volts: 12
Oil capacity: 1.75 qts [1.7 L]
Sparkplug: NGK BMR-4A
Sparkplug gap: 0.025 inches [0.635 mm]

Kawasaki FB460V engine. A free PDF manual for the engine can be obtained at "my mower parts dot com" (but translate that into a genuine URL to get there).
OP still has not confirmed if this tractor has a electric PTO clutch but some internet searching indicates it likely does.
While it is not typical for a BELT DRIVEN blade drive system to result in shearing or bending of a flywheel key it is certainly possible that in this particular case (lift arm disengaged and dropped deck assy) the stopping of the blade belt was abrupt enough to shear or bend the flywheel key.
Usually a belt driven blade system (and thus the engine crankshaft) will not stop turning quickly enough when the blades encounter a significant foreign object to cause shearing of the flywheel key. The saving grace in belt drive systems is that the belt usually slips enough that the inertia of the engine is absorbed relatively slowly......and the key survives intact.
However.....in the case of the deck being dropped downward suddenly by the lift link letting go......the belt would have been given an added bit of tension (by dropping too far down) and that just might have been enough to shear the flywheel key.

I was looking for a 1121, not a 112L!

IF it doesn't have an electric PTO, the attachment switch would likely be a 2 wire switch that is activated by the position of the "engagement" lever.

To engage the blades, do you pull a button or move a longer lever?

***"I was looking for a 1121, not a 112L!"***
Me too until I saw the C&P spec sheet.

Sorry for the confusion regarding the model number. Yup 112 L. The PT switch is on the dash. It is about 1-1/2 inches long n sticks straight up with a little yellow plastic sleeve on it. I just toggle it forward about an inch and it engages the blades. That's when the mower stopped and the deck lift lever disengaged from its button anchor on the top of the deck. Thank you all so much for your responses. This may wind up being over my head. But it's good to know.

I called Deere n ordered an operators manual. I bought it used for 450.00 with under 300 hours on it, 10 years ago. But no manuals. Again, I just use it as a second mower when it's too wet for my xmark. But this has been incredibly loyal with basic maintenance.

It sounds like you have the electric PTO.
I don't have any Deere schematics, but-

Typically, the PTO will have 3 functions-
1. Engages the mower deck
2. Engages a safety circuit which requires you to be in the seat when the deck is engaged or no spark.
3. Requires the deck to be disengaged when cranking.

Usually, the 2nd function is used in conjunction with the seat switch.

You pretty much need to check for spark when cranking.
IF none, I'd check the seat switch. Make sure the connector is plugged in firmly. Some tractors WON'T run with it disconnected.

You can also try priming the carb with 2-3 teaspoons worth of gas and see if the engine tries to run. IF it does, it's a fuel issue.

Thanks again all. I'll check for spark tomorrow. Then I'll check the wires coming out if the PTO. Looks like two plastic boxes. One with 2 wires and one with three. I'll be in touch.

Mownie, if it was the flywheel key would it sound totally normal while cranking? Cause it does.

Yes, it would sound totally normal..............unless the flywheel has skidded so far off the keyway that it causes a backfire out the muffler.
A sheared or bent key will not prevent the spark from being made........it just causes the spark to occur at the wrong point for the engine to utilize it.
But you need to confirm if it actually has a spark before taking the flywheel cover off. If you have a notion of trying this yourself you need to download a free PDY service manual as I mentioned earlier, the Deere Operators manual may not be of much help for engine questions.

Ah, a 112L . New one on me. I might accidentally have a service manual if it comes down to it.

If you have one, I think its an antique and will probably fetch a few bucks.

I worked on it on n off Saturday, all Sunday and Monday nite. So today I'm having tractor supply pick it up. I'll save myself more headaches n let them sharpen the blades, change the belts AND fix this problem. Other than a new coat if paint, it ought to be like new. Will let u know what it turns out to be. Thanks again