Disclaimer: I am only familiar with the Canon 40D and the below is a suggestion only. Double check before doing anything.
The shutter release cables are non-powered so triggering the shutter should be the same as for the Canon 40D; close the connection to activate.
On the 40D although the shutter triggers by shorting only the trigger connection, focus is required for other things like mirror lockup and bulb mode. The same behavior is found on other cameras as well. This is why I always advise using both the shutter and focus triggers even when you are not using focus. If you look at remote shutter release cables, you will see that they close the focus connection as well as the shutter connection.
To test, you can manually close the connections and see if the shutter triggers. You just need a jack and some wires.
- This reply was modified 3 years, 2 months ago by Martyn.