Area 51 ALX Motorized Door Not Working, Missing cable

Hi. Area-51 comes in two versions and three color varieties, the two non-ALX are called "standards" (rather "STD" in their build sheets). ALX models have matte Space Black exteriors & the inside of their door panels are also black

That's a nice photo of the ALX matte finish. The standards are bare aluminum inside as the easiest way to tell (open the door & check). If you have a Lunar Shadow grey-silver model then it outright can not be one

Most often the deep-purple metallic flake semi-gloss Cosmic black is easily confused but if looks could kill ... 

The desktop you bought is the standard non-motorized version that uses a brass tensioner & a simple gear-rod-axle so it's settled then ... to truly be happy you have to own all three color-types ...

Dis & reassembly of the front panel "bezel" can be difficult, do take care of yours, the ribbon cable is the most delicate part & must be reinserted in such way that when the other parts go back in, it doesn't get, well, chewed up or otherwise harmed when the panel drops & lifts

{Remove coil & gear-rod to convert standard Lunar Shadow into a Bionic Beauty}

The motorized version has the identical gear-rod-axle but applies a larger gear (left) to turn the central mini-gear. Therefore the "ALX" is simply an anodized matte black finish w/ exclusive use of a motorized front panel system which includes:

• motor w/ cable + push-button switch under the Alienhead + MIO board 

Below, standard MIOs haven't the necessary header connector & SMD components: all the "ODD Motor" circuitry in this area is bare & "unpopulated"

"Standards" are missing what's shown in my personal sketch below, ie the 4pin connector, smd "stuff" (as well as the tactile switch living under the Alienhead)

Per your photo, all models get an ODD Switch1, it's for their front panel internal limit switches to plug into; ODD SW is so they can all turn on (or off) panel LEDs when the door opens-shuts & for ALX its ODD limit switches also kill DC 5V when the motor's fully down or up

With motor & cable, standard MIOs can't plug-in nor work

I'm aware it's kind of like thinking you bought a Z28 or TransAm because the owner "said so" just to discover later on it's a base model, in fact I was highly surprised ("shook") when I learned my Cosmic Black wasn't motorized. The cure was to learn their differences & go looking for an ALX for sale (I got mine from Dell's eBay store of all places). Below I'd went to Dellware.com & ran their Service Tags (they all say ALX on the splash page), Qwik Links > Prod Specs > scroll down to the chassis line item to find out what the original owner ordered ... I hope this helps?

edit: @ Red ... it helped when support looked like below

Late Edit:

Above, in certain light the dark purple sparklies on my Cosmic Black unmistakably pop while the one below puts the black in Cosmic Black (so much so it's ALX-passing ... but the shine gives up the game)