Here is a guide to modding the N64, covering how to open it up, remove unwanted ports, relocate the game cart port, video, powering the system, trimming the board and advice on other relevant matters about modding the system.
PLEASE NOTE – if you are interested in this section, please also see the N64 Video Guide Logs!
The section had to be broken into chunks as otherwise the .PDF’s don’t work.
If you want to select between running system off mains power and batteries; here is a way to do it. If recharging, make sure the system is off first.
N64 board trimming
You can reduce the N64 motherboard along the bottom and sides with low risk, and only needing to relocate one component (the LED). All you are doing is missing the components and traces on the board and removing the grounding mostly, leaving just enough to maintain contact around the board areas. If you cut the board just under the LED contacts then obviously you don’t need to relocate that component.
There are more things you can trim off, although will need some wiring to tiny capacitors (eg the power pin area, a/v area.
You can also trim a tiny amount off the top (by the game cart) through the middle of the 12v line, only needing to connect a wire between ground on each side of the board; however, did the below to keep it simple to reduce the board a bit without making it hard. Click on images for full-size.