Slave manual (non-TTL) mode with S&S YS-D1?

I know the slave TTL mode is available and works well. However, is it possible to get manual mode (set the power of the strobe to be fired) in slave mode?

Also, does anyone know where the slave sensor is on the YS-D1?

The YS-D1 slaves via a fiber optic cable. The port for the slave function is on the bottom of the strobe, just forward of the port for the camera to strobe fiber optic connection port. Manual control of the strobe is possible when using the slave port.

I should mention that the YS-D1 slave function is not a remote off camera slave, but a slave function off of another connected strobe.

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.

Mark, have you tried your set-up in the water with the sun shining? I have found that trying to "remote" slave fire my D1's without a cable to be unreliable.

I have not tried it underwater yet but am using my strobes for some limited land photography and would like to use them with optical triggering and manual control.