Jim Stolis and I modded my Expansion Module #2 for ColecoVision to add an indicator light and power to bypass the need for four C-batteries:

I added the key switch (unfortunately a chinese toy-switch that operates in the wrong direction) but I think it’s still pretty cool!

I also added a second primary fire button for one of my already modded ColecoVision controllers.  This gives me the ability to button mash on games like Defender: