I picked up this Westinghouse OV25 last summer, decent shape minus the missing door for the input connections. What I'm unsure on is the input voltage of the ballast, research says it should be a 400w 240v fixture amd I don't doubt that's the original ballast, hooking it up to 240v the lamp lit but quickly tripped the 20amp breaker. Thinking it was maybe 110v I tried that and it not light and eventually tripped the breaker. Feeling stumped.

Since I don't see any capacitors in there I'll assume your light has a choke style ballast which means it's either 240 or 480v  More than likely , 480v .

That wouldn't explain the breaker tripping?

Do you have any better pictures of the ballast?

The primary appears to have fairly thick insulation, perhaps It's meant to operate on a series circuit https://www.lighting-gallery.net/gallery/displayimage.php?album=1006&pos=63&pid=30628. 

 Try connecting a big incandescent bulb in series with the primary (the lamp might be damaged from the first test).

I know little about ballasts but I just want to say that is a beautiful fixture.

The wires I pulled out of the terminal block on the input side were 8 or 10 awg. I'll stick the bulb in one of the high bays I have and see if it's still good.

The capacitor would be to correct power factor correct? I wish i hadn't fried my control voltage transformer as it had a 480 tap. But it would make sense as the higher voltage would lower the current.

 This street light  runs in series 6.6 A or  20A series circuit.  Reason for thick heavy inslation because 3 to 6 thousand volts
 Going in series.   If it 6.6 amp it would  drop 61-62 volt  if  it a
 400 watt  mercury ballast.  Being on 240 volt  it did some damage to it windings,   20 A would see 20 volt drop in high voltage series circuits.   Next  time u find street lights like this
 I would ask questions before u do anything.  Like putting 6..6 amp of 120 volt worth of incandescent bulbs in series with this ballast. 

Just because I didn't consult with YOU (funkybulb), doesn't mean I didn't do any research.

Ummm.   I kinda chime in as  none of other lighting folks on here could not figure this one out.   Anyway that ballast prolly  toast.
 As it felt 240 volt on it  ballast.  Anyway it a series ballast that
  Use a one wire feed  that goes comming into and out of ballast
  To next street lights.   Airport lighting is one of last series system  anyway there still seires street lightng in use
  And still running HID.   But it slowly getting removed and converted over to parallel wiring so city can use leds . 

  I have some 175 watt 6.6 A HID ballast in my collection as i want to make a 24 volt mercury vapor that runs off grid power .