With a SECU16 that has a version 10 PIC, activating pulse mode makes all relays that receive an ON command respond by turning on for a short, precise time interval. The ON duration will be the same for all relays, namely the value of parameter 5 * 13 mSec.
One thing to be careful with is that the controller always sends an image of how all outputs should be set whenever any command is sent to the SECU16. So if you have code that turns on Relay #8 and then a bit later you turn on Relay #9, it actually "updates" the module to tell it that realys 8 and 9 should now be on. This is not a problem in regular mode but in pulse mode, any output that was previously set to on will pulse again. For that reason, it is a good idea to program your routines to turn off all relays being used and then turn on the one you want to pulse. It is also not necessary to first turn off an output in order to have it pulse again by sending another on command.
When pulse mode is enabled (done by setting parameter 5 of the SECU16 to the desired pulse time interval) all 8 ouput relays will now only work in pulse mode, you can not have one turn on and off the usual way with the correponding "Then Module/Point" on and off commands. You could however have some SECU16s in pulse mode and other ones in regular mode . Check which PIC version you currently have by looking at the module listing in the controller access screen. If you already have version 10, then all you need to do is edit parameter 5 to set it for the desired time delay, where pulse time = 13 mSec * parameter 5. For a one second pulse, you would set it to 77. When editing a module parameter, the "password" field must be set to the value of parameter 6 of module #1.