TTL is a little confusing. On page E12 of the S&S YS-D1 manual:
When a fiber-optic cable is connected, DS-TTL mode is activated.
(You can switch to Slave-TTL mode by pressing and holding down the target light switch for 3 seconds).
I have done this and it works well with no fiberoptic (or otherwise) connection of the strobe to the camera. However, I would like to achieve manual (non-TTL) activation of my 2 YS-D1 strobes without the TTL function so that I can adjust the strobes as needed.