I soldered wires from each one on my n64, I also made up a second cartridge port with the extender ready to solder to another n64 just incase I decide to make another.
I had 3 n64s! ha ha!! Now I have 1 working n64 and 2 part boards though
I've learned a lot about the n64 though in that time. Also, the 2 n64s I ruined are ones that I bought for $10 a piece on ebay, and the one I'm using currently I got for free from a friend.