EC18 pin 16 is channel 5
Channel 1 is not normally connected on a standard Vems box. It is internal and connected to opamp 'Diff B' which is maybe why you can see the voltage you do.
EDIT!!
The above looks to be for older versions of V3. The latest version suggests that EC18 pin 16 is indeed channel 1. That said, channel 1 on the V3.6 is still on Diff B. Try a different channel number on EC18 pin 2, 3, 6 or 12, channel 5,2,6,7 respectively all of which appear to be pull up to 5v.