About all you can do to eliminate the interlock module as "THE CULPRIT" is to physically disconnect any/all electrical loads that feed from the interlock module.
Essentially to test the condition of the interlock module, you have to disconnect everything powered out of the interlock module so that a short in the fed components can be ruled out. Headlight switch wiring (from interlock to headlight switch) and PTO switch circuit are some of the circuits that lead from the interlock and a short in those wires can blow a fuse. Other circuits include the seat switch and brake switch circuits. You will have to actually inspect the entire wiring harness for physical damage (chafing, burning, rodent chewing) and not just unplugging connectors from switches etc.
If, after all the things that feed from the IM are disconnected, the fuse still blows, then the IM likely is shorted internally.
Do you have the Deere schematic for the electrical system?

I inspected the entire wiring harness and found no chaffing nor rodent damage. Fuse still blows when the X4 connector is plugged into the circuit board and seat switch is closed, even though every component and switch is disconnected. BTW, is the interlock module the same thing as the ignition unit that is a circuit board where the key goes in?

Yes, the key switch is integral to the interlock module.
Can you take the seat switch assembly loose from its mount and operate it manually in your hand?
In the Deere manual I see a Pink wire 800 and a Yellow/w black tracer wire 414 connecting to the seat switch. Yellow/w black trace is the power feed to the switch FROM the interlock module while Pink 800 is the seat switch signal wire feeding into the interlock module FROM the seat switch.
If the seat switch is somehow shorting to its mounting when operated........removing the switch from its mounts and operating the switch in your hand would eliminate the switch itself as the fuse blowing defect.
The Deere diagrams leave much to be desired (at least the one I have does) as it does not show the complete circuitry on one page, so you have to infer a few circuits that it does not show explicitly.
If the fuse continues to blow with the seat switch unmounted, and you have sure enough disconnected all other loads that feed from the module, and no shorted wires exist anywhere in a harness...............that seems to leave the Interlock Module to be shorted internally to itself.
If you are looking at the same Deere literature as I am there are some tests that can be done to various components/circuits.......but those tests relate to things being inoperative in an otherwise OK electrical system.
This is not the case with your problem.
If you could isolate Pink wire 800 from the Interlock Module and then operate the seat switch as you described would be a big help. If taking that Pink wire out of the picture right where it enters the IM stopped the fuse blowing it would confirm that the problem was related to the Pink wire. Then you would have to determine if there was a short somewhere in the Pink wire between the seat switch and the IM.

The Deere manual describes that there are 2 configurations of IM used on the LX176. One type has 2 separate relays and the other has a single large double relay.
Can you unplug either, or both relays and then repeat your tests with the relays out?
I too am not exactly sure of how the IM goes about its business but relays MUST have a ground in order to operate and it might be that a relay is defective and when it operates (seat switch signal) it "goes short to ground" instead of its intended function.
I also "see" a couple of diodes in the IM and sometimes a diode can become shorted and (under the right circumstances) permit a normally denied circuit path to be conductive in the wrong direction.......which usually means that a "short to ground" is created.....exactly what the diode was supposed to prevent......and a fuse will blow.
It would seem that you have done a thorough job of testing the beast and unless you see some results with the relays........you might have to cross your fingers and buy the IM.
Unless a Deere dealer has a better way to determine IM failure it looks like you have arrived at the only conclusion possible based on the tests.

My IM version (AM120105) has one relay and it is soldered onto the circuit board. Same with all the other components you see on the board so it doesn't seem like there's much more I can do. I don't see any mechanical or visible breaks or defects in the circuit board - it may just be something mechanical inside the key unit that's soldered into the board. I just ordered the part.

Thanks for your posts - they were very helpful and much appreciated. I'll post the result when I get the part or otherwise get the problem diagnosed and fixed.

Success! It was the interlock module. A new one did the trick. So glad to get the tractor working again without having to pay $300 for a service call - it's a well built piece of equipment that has served me well for 12 years and hopefully many more.

If anybody has a similar problem, hopefully this thread is helpful.

Mownie - Thanks again for your very helpful posts.

THANK YOU for posting the success story sir. Kudos to you for sticking with it. :^)

Hello. I just had the same thing happen to my sixteen year old 176. I went over a bump, and no more engine. I tore the tractor apart and inspected all of the wiring, to no avail. I checked the interlock board, again, no problems. I replaced the fuse, and all is working, except I have not yet reconnected the PTO clutch. That is tomorrow's job - check it and connect it. I will post my findings. My local JD dealer told me that if the seat bounced, the PTO clutch may have been momentarily disconnected and that can cause a EMF spike, causing the fuse to blow. We'll see. By the way, the headlights are fed through a separate fuse - for future troubleshooters.

I have a similar type of problem.

Gene06883 , Can U help me explain what can be wrong.

Fuse 05 Ignition Run Power fuse blows. John Deere 3720

My LX176 runs for 10 /30 seconds then dies. I have spark then no spark. I changed the ignition module with no luck. I am hoping it is a bad coil.

Just wondering if there is a way to by pass the ignition circuit board if it is bad?

If there is no ground sent to the coil, it should stay running. So if you have put an igniter on and you unhook the kill wire, the stall would be on the coil.

Has anyone had any problems with a 5093e John Deere tractor not going into ForForword AR reverse