I have a Mitsubishi Diamond Pro 900u, which is the direct predecessor to the Mitsubishi Diamond Pro 920, which is what the ElectronBlue 19 I is. Most likely the connector locations have not changed, and you can't really harm anything connecting them wrong.
On mine, from L to R (as seen when looking at the back of the monitor), the BNCs are
R, G, B, Horizontal/Composite Sync, Vertical Sync.
If you have a cable with 5 plugs, connect them all. If you only have 4 plugs, leave the Vertical Sync empty.
tooki