f500bt operation manuel says about 5v jack "Use this jack only to connect with the AC adapter" in page 12. So if i dont misunderstood i can not use this jack with lighter adaptor!!! is it true? if it is true i think it is so nonsense. 5VDC is 5VDC. it is not important where is it came from.
5v is 5v, I don't think there is enough difference, which affecting the operation of F500BT, between the 5v provided by the A/C transformer, and the one provided by the cigarette adapter. Yes, there are difference between the AC-DC and DC-DC coversion, but it should be ok. I didn't test this systemactically, but I did connected the cigarette adapter directly to the left side of the F500BT once, and it works.
I dont want use this fat cable because i will not use suck mount. f500 is so big for use in front of windshield. i have laguna and i will put f500bt in front of my radio.
I didn't use the suction mount niether. I mounted the cradle to the front dash using a modified Vent mount. Keep in mind that the F500BT doesn't have any mounting hole at the back, the mounting holes (a standard 4-hole mounting system) are on the back of the cradle.
Here is how I mount my F500BT:

