The relay leak current on the signal pin. Instead of reading 0 volt and 5 volt on low and high state, I read 2.6 volt when nothing is connected on both signal pins.
If both channel are high.... It move into trouble zone (so better not going there)!
Uhm, this sounds normal. The control circuit has a current limiting resistor, a visible red LED and an IRLED connected in series, so with nothing connected, 2.6V sounds correct. Did you know that as a test (with Arduino control outputs disconnected), you could just short any relay input to GND to activate it?
What trouble? It should be OK writing both HIGH.
The switching still work when I disconnect the + pin and the GND pin but will the Flyback protection will be active?