What is the best way to load a sound effect that is 17 seconds long that I want to run start to finish for live application.  I have it as a .wav on a flash drive?  Will it be saved internally?  Thanks in advance.

The best way is to load it to a KEY in a DRUM KIT VOICE. The reason is a drums, unlike most keyboard sounds, are designed to be able to play from start to finish without having to hold your finger on the key. Drummers do not have duration tied to continuing to remain in contact with the instrument. So Drum envelopes can be set to trigger and hold a sample for as long as necessary.

This is gone over in detail in the following SUPPORT article:
Drum Kit Loop Tutorial

Of course you can set it up to play once (or loop) it is your choice. If you get stuck post back here.

I have it as a .wav on a flash drive?  Will it be saved internally?

Once you load the sample to internal memory - which requires that you add DIMMs to your XS (see page 295 of the Owner’s Manual for details) the sample will be apart of that Drum Kit Voice. Samples are placed in volatile RAM, which means when you power down they disappear. So you will want to load the sample to the Drum Kit, then [STORE] the VOICE to a USER DRUM location, and then make a backup file in Motif XS format

Place your USB drive in the slot
Press [FILE]
Set TYPE = ALL
Press [SF1] SAVE
Give the file a name…
Press [ENTER]

you will need to load the data next time you power up - or you can make it an AUTO LOAD file, in which case the XS will load your file automatically on power up.

Thanks.  I’ll try this when I get home from my boring day job.