Hi, marvin, welcome to the HiLo family!
No you do not pull the cable twice. It is a safety bar release that gets the safety bar out of the way so you can lower the top. It is not pulled at all when you raise the top.
Now, what you call the black toggle switch is probably the Master Switch (MS). It has three positions:
1. One end IN allows the top to be raised or lowered with the White Switch.
2. The other end IN gives you full power to all interior electrical equipment (lights, fans, water pump, furnace, etc.)
3. Center position locks out EVERYTHING (for traveling) except the refrigerator DC power.
I can't be specific on which end does which because in some trailers the switch was wired backwards. BUT if you have interior lights with the MS depressed at the top, push the bottom to be able to move the top. (And vice-versa).
Now, to raise the top, just place the MS in the raise/lower position and press the top of the white switch. You will hear the safety bar slide in place just before the top stops moving and the lift motor sound will change.
To lower the top, again place the MS in the raise/lower position. Then pull the cable to release the safety bar and press the bottom of the white switch. Once the top starts down, you can release the cable.
There's one possible minor change to this that you will have to employ if the top has "settled" on the bar, binding it. If you find you can't pull the cable out, simply raise the top off the bar while pulling on the cable. Once it releases the bar, you can lower the top.
There are a whole set of videos that you can watch to learn all about the HiLo. Here's the link to a thread that has all of them, starting with Post #3:
http://www.hilotrailerforum.com/f49/hilo-video-owners-manuals-youtube-1233/ Number 5 covers raising and lowering the top.
Hope this helps.
- Jack