Connecting a zone expander, like the 4219 or 4208SN, is relatively easy.
There are two possible ways to do it: using the terminal block or the 4-pin console plug. You have the option of connecting either or both, it doesn't matter which.
Here's how to do it:
Connect the 1st terminal/pin on the block/plug to control panel terminal 7.
Connect the 2nd terminal/pin on the block/plug to control panel terminal 5.
Connect the 3rd terminal/pin on the block/plug to control panel terminal 4.
Connect the 4th terminal/pin on the block/plug to control panel terminal 6.
When using colored, four-conductor alarm wire, connect:
1) Yellow to expander block/plug terminal 1 and Vista 20P terminal 7 ("Data Out")
2) Red to expander block/plug terminal 2 and Vista 20P terminal 5 ("Power")
3) Black to expander block/plug terminal 3 and Vista 20P terminal 4 ("Ground")
4) Yellow to expander block/plug terminal 4 and Vista 20P terminal 6 ("Data In" label)
And finito! Your zone expander is now connected!