My apartment complex was converted to LED   back in March 2014 and I was able to get a hold of one ballast and lamp (Of course I got a busted cap and a castor lamp)   
I got for the price of shipping an empty Stonco FloodPak and a GE Multivapor M90 lamp from Alights (Thanks BTW). After all of these months I am finally getting around to trying it (I bought a new capacitor from eBay) and I think I wired it correctly as I had to replace the capacitor and I did not have a socket at the time I received the ballast but the FloodPak fixture has a 4KV pulse rated socket. So I replaced the capacitor and wired in the socket and a grounded power cord but I am nervous about plugging in the fixture (Fearing that I wired it into a direct short) as I tested the hot to neutral and I get about 8 Ohms (So I think the ballast is bad??, or I wired it wrong?) I get the open circuit reading from hot to ground and from neutral to ground

I am a newbie when it comes to HID ballasts so I don't know if what my meter is telling me is wrong or not (If the ballast is good or I wired something wrong)

The ballast is an Advance/Philips 71A5380

Here is a picture of the ballast as received


Here is a picture of the busted capacitor


PS: I believe the ballast and ignitor (The capacitor is obviously bad) to be in working condition as the post top fixture was illuminated the night before

The resistance reading you got should be fine. A magnetic ballast is simply a couple of coils of wire. And naturally, the resistance across a bunch of wire is going to be close to zero. By measuring between hot and neutral, you're simply measuring the resistance of one of those coils.

If you're nervous about if you have it right, stick a high wattage (at least a couple hundred watts, if possible) incandescent bulb in series between power and the ballast. That way if there is in-fact a short, the bulb will limit the current. Of course, the metal halide lamp probably won't run up all the way (or if the incandescent bulb is too small, the MH lamp might not even start). If everything is well, the lamp will start, and the incandescent bulb will just barely glow. Or you could use a fuse.

Trent

If you're afraid of the possible outcome, get a long extension cord and fire it up outdoors where you can observe from a safe distance.

If it still wont fire up test the ballast by screwing in a crap
Mv lamp to see if it even starts, if so the ignitor  is bad as it send 4 kv to oulse start lamp.

OK I finally got around to plugging it in I plugged it into a switched receptacle and I then went and turned on the switch (Yes I am a wimp when it comes to electricity)
and the Metal Halide lamp fired up on the first pulse of the ignitor and for a 100 Watt lamp it is bright. Thanks for the reassurance that it would not blow up on me

Now that I know it works I have a question about the UV output of the lamp
The lamp I am using has many warnings about UV and eye and skin damage and I obviously do not want any of that. I believe the glass of fixture blocks most of the UV radiation? I think I have the FloodPak Medium model but I am not totally sure as the model is not any markings on the fixture except "Use 150 Watt M102 Lamp Only" (That warning was for the original ballast as I got the fixture empty and I installed my M90 ballast)

Thanks

Your lamp does not emit harmful UV as long as the outer envelope is intact. In case of breakage it's another story. The greatest danger of metal halide lamps is arc tube rupture. As long as the lamp is fully enclosed in a suitable fitting, there is very little danger. Open rated lamps are virtually the same as standard lamps only with a thick glass tube that surrounds the arc tube to contain the fragments should a rupture occur. Since you stated you are operating this in an enclosure (even if it is rated for 150 watts ; your ballast is rated for 100 watts and so is your lamp) you should have no worries about the UV. Enjoy your new acquisition and welcome to the world of metal halide !