Well, I have connected the source pin to the input of a seperate voltage regulator. Regardless, the measurement is still 1.3 volts. Same as if I left the pin floating.

Should I be using a P-Channel device instead?

The ON resistance isn't a big worry, If there is a bit of drop within the device, I'm fine with that. I just need to be sure that in it's OFF state, there is little to no current usage.

But why would the source, when connected to a seperate linear voltage regulator (LM2941), measure only 1.3 volts when ON?

Thanks
Steve