Where does the negative battery cable connect to the mower on the John Deere D105 Auto?

This is your transmission here and it says what models it will fit.

https://www.lawnmowerpartsworld.com/home-garden/complete-transmission-rt400-gt87140-john-deere-auc11077-auc10266-d105-x105-e100/

The LT155 looks similar, so if you have one, try it.

https://www.ebay.com/itm/144684745738?hash=item21afe2040a:g:inEAAOSwHr9iTEuy&

https://www.google.com/search?q=John+Deere+D105++transmission+VS+John+Deere+LT155

..

https://video.search.yahoo.com/search/video?fr=mcafee&ei=UTF-8&p=D+105+transmission+john+deere+mower+slow&type=E211US1494G0#id=4&vid=3c0ad4f41b214eca83a875a8c04c9731&action=click

This may help

Contact John Deere directly to request the diagram.

For sale online:

https://www.ebay.com/itm/John-Deere-D105-D125-lawn-tractor-technical-service-tech-manual-on-CD-TM113219-/371119412974?_trksid=p2349526.m4383.l4275.c1#viTabs_0

John Deere D105 D125 lawn tractor technical service tech manual on CD...

look on google with make and model or john deere website it will give you blade size

LT190 - Operator's Manual - John Deere

manuals.deere.com/cceomview/OMM152795.../OMM152795_H46.html
Disconnect spark plug wire(s) or battery negative (-) cable to prevent engine from starting accidentally. · Always wear gloves when handling mower blades or ...

Sparking between the lead and positive terminal when connecting them is normal. But you should always connect the positive first then the negative.

It floats?? but the carburetor still leaks fuel ????
Fuel is HIGHLY COMBUSTIBLE! Please read the safety notes in your owners manual before attemting this repair. Lawn Mower Carburetor Repair Small Engine Maintenance Briggs Stratton

does it go in reverse ??? if no, suspect the belt, or did you have the wheels off of it recently ??? if yes then still suspect the belt or a bad transmission

Yes, you can jump start it with any 12 volt battery on any vehicle. Just do not have the donor vehicle running. Connect the positive cable from the donor battery to the positive post on the battery on the mower. Then connect the negative cable from the donor battery to the engine block or other ground source on the mower. Do not connect it to the negative post on the battery. Make sure you have a good connection on bare metal for the negative cable. Disconnect the negative cable the instant the mower starts.