sbrown:
I bought a new arduino and added a resistor in series with the 5V output as you suggested
That isn't what I suggested at all.
I never said to use 5V as a signal source.
In fact the suggestions I made were all about NEVER using 5V or even an Arduino pin set to HIGH as a signal source.
Pins set to input will read whatever "signal" they are receiving, no?
Correct.
If pin 3 reads HIGH because I'm supplying voltage to it, but then I remove the supply - does it stay set as HIGH? I figured it would now read LOW.
Based on what you just said you are doing above, (connecting an Arduino pin in INPUT mode and changing the Arduino input pin from being connected to a signal that voltage supplied to it (which should read as HIGH) to not connecting the Arduino pin to anything, the Arduino pin could read anything and will likely bounce around between HIGH and LOW since the input pin is changing from being connected to a high signal to floating and floating is undefined.
You seem to still not be understanding some very fundamental electrical concepts.
It also seems like you are either not reading or not understanding some of the recent posts about how to not use 5V as a signal source.
My suggestion would be to quit playing with the Arduino and take a big step back and spend some time reading and learning some electrical fundamentals since it appears that your current level of electrical understanding is a bit below what is needed for a project like you are attempting.
--- bill