Engine shuts off when put into gear

Those ground wires can be causing all of your electrical problems they need to be connected. Where is the other side of the cable? Clean the cable connections before installing them. Clear the codes and try again.

Please let us know what you find.

Cheers, Ken

The large one goes to the engine and the small one goes to the frame/body. Can you take pictures of the other end so I can see to be sure?

Those are both grounds. One should go from the frame to the engine, the other goes from the engine to the body. In this case you have the middle point where both of those attach to the frame. Does not really matter where you attach them as long as it is a clean connection with no paint or rust and they can flex as the engine and body move around. Does not matter if the braid is oily, as long as the rings are clean where they meet the other parts.
With them loose as they are you will get many strange electrical issues as well as possible parts failures in what seem to be unrelated parts. This is due to the currant from the battery seeking to find a path to complete the circuit back to the battery or from the alternator though its circuit paths.

From the first picture they were either both bolted under the cable clamp or in the hole to the left. Either will work as long as you clean the rings on the braids and the spot on the frame.

Nice work, we are here to help, please use 2CarPros anytime.

Cheers, Ken

Great to hear you solved the problem. One of the mantras an old gentleman I knew always said when presented with an electrical problem - "Check the Grounds". These days it is even worse due to all the electronics on the vehicles.