Will an NTSC N64 Rumble Pak work in a PAL controller?

Solution 1:

The following information doesn't seem to be easy to find so hopefully the following information can answer other questions.

N64 game controllers and Rumble PAK's are not region specific. They all send and receive the same commands over the controller wire.

Technically the N64 Mouse could be considered region specific because the only games that used it were released in Japan, but internally there isn't any region limits. It sends the mouse movements instead of joystick movement and the left and right buttons are mapped to A and B, the game can tell the difference so the mouse isn't a drop in replacement.

The Memory PAK's are not region locked in the usual sense, but may contain Save Game names that are not readable without for example a Japanese or other regional font being available.

The Voice Recognition Unit (VRU) is Region specific, I've plugged in the Japanese VRU (aka VRS) with the US version of "Hey you, Pikachu" and received an error message that it was the wrong unit. Which makes sense since it's a very language specific device.