So after some digging I was able to locate a Sylvania 100w mougl base dx MV bulb from a local electrical supplier. It took some persuasion with the person on the phone as they always try and sell me MH and HPS retrofit gear but the counter person was able to get me what I was after.
 
I also ordered a new twist lock photocontrol socket as the original "Landmark" Nema MV fixture photocontrol sockets wire insulation was crumbling off due to years of dayburner heat lol.

So if I got this right, I disconnect the three wire ignitor and two wire capacitor from the magnetic 70w MH ballast  to run my 100w MV bulb in my Nema fixture?  This sounds like its a reliable set up and should operate for years in a dusk to dawn type useage.

Aso, do they make a fisher peirce style photocell thats less ligt sensitive? I have a fiew older photocells but my Nema fixture comes on to early and shuts off to late.

So basically I need one that would need to see very dark light for it to close the circuit and turn the fixture on and subsequenly need to see very little light to turn the fixture off.

Thanks for everyones help.

Disconnect just the ignitor, keep the capacitor. And it is sufficient to disconnect just the lead connected to the Neutral, but if you are not sure which wire is which, disconnecting all three (and storing the ignitor inhouse for an eventual future use) is better than just guessing...

Otherwise for the photocell: Look inside, in many older designs there is a metal shield blocking art of the light, so it comes ON earlier and OFF later, you just remove it and keep all the light in.
Or in the case of new, electronic type, there use to be sometimes a trim-pot to set the sensitivity...

Ok sounds good. When I dissasembled the indoor 70W MH floodllamp the 2wire capacitor was wired in paralell with the lamp or socket, it this how I should rewire it using the 100w MV lamp?

I pretty sure I understand how an ignitor works and its purpose but what is the capacitor used for on HID lamps?

Just fallow the wiring diagram on your ballast
And just disconnect the ignitor

My 70 watt ballast had power factor correction
Cap that across the Hot and N  and ballast lead directly
To the lamp socket

There others that have caps in series with the ballast

If u just fallow the wiring diagrams on the ballast and
Disconnect the ignitor. You should be good to go
For MV set up from Mh ballast.

The cap should never be in parallel on the lamp put out leads. Can  u show pic of the wiring diagram ?

There only two places where a cap should  go
In series with the lamp as these would help
Regulate the ballast current of CWA ballast
Constant wattage Autotransformer

2nd place is taking a HX ballast normal power factor
Ballast as the current lags the mains voltage
Causing  twice the power draw for the power plant
But your home electric meter wont see this as it will
Read same wattage for the apparent power used
So the cap is  place on hot and neutral just before
It enter the ballast to correct the power factor bringing
The current back in phase with the voltage making
It true apparent power to keep the power company
Happy as they wont penalize  the business for bad power factor.

 

Yepp sure enough I wired in the cap incorectly and I hope this didnt do any damage to the bulb or ballast.
So after finding the wiring diagram on the ballast it shows to wire the cap in paralell on the line ine wires before the ballast.

So I will try this again and see what my results are.

Thanks for your help.

After removing the cap and installing it correctly this time the 100w MV bulb seemed to operate much better on the 70w MH ballast. Thanks for everyones help as this was fun building a custom one off 100w MV Nema head fixture. I have access to about 15 70w MH ballasts for about $20 a piece so I could build a fiew more.

I will post some pics of my light install in my backyard in the next hour or so.

The only issues Im having is how long the light is on for from dusk to dawn. It comes on to early and shuts off to late! The fixture is up high in the tree line but the photo still gets ample light to the window. Do they make a photocell thats more or less sensitive to how much light it needs to see before it operates?

Many photocells have a shielding plate in their "eye" designed to block part of the light, so it come on earlier. If you want it to come on later, just remove that shield. Frequently it is in the form of a perforated metal plate, or a solid piece partially shielding the CdS photo resistor.