So I have plug in cords from my ballast to my sockets. My thousand watt hps works on both cords but my metal halide will not work on cord that my hps does. Could it be a polarity issue?
2 Likes
I’m no electrician. Electricity is one thing I’m extremely weary around, it usually only bites the once.
That said, have you checked the basics, which is about all I can help with.
The mh bulb itself is okay?
Can you try it with another ballast?
The only mh that I ever used hung vertical as opposed to the horizontal hps bulbs I’ve seen. Don’t know if they can be used on the same ballast?
Like I said, I’m very weary of electricity, but we have some bright sparks here (pun intended) that will be along and be able to give you better advice than I can.
5 Likes
Ya step one is test that ballast with a different bulb, and/or that bulb with a different ballast. An HPS ballast will fire an MH bulb of the same wattage so you could even try like that.
3 Likes
from the ballast to the lamp fixture (bulb) correct?
same question?
on both cord sets? is the bulb known to be good that is not lighting?
probability not
what type of ballast? digital ? magnetic?
what type of bulb single ended? double ended?
post a picture of what you have and I am sure you will be helped
all the best and good luck
Dequilo
3 Likes
This was already asked, but is the cord from the wall power to the ballast or the ballast to the bulb?
If you are trying to use the same ballast for both bulbs, then thats probably what is wrong. Most ballasts only work with one or the other - not both.
If the cord is running from the wall to two different ballasts - one for the HPS and one for the MH, then it might be a problem with the ends of the cord - worn or loose contacts etc.
Yes. This will clear things up.
2 Likes
most digital/electronic ones work with both
a picture would help a lot
all the best
Dequilo
3 Likes
I agree, My 400w HPS AIO fixture requires a special 400w MH conversion bulb to be able to be used in the same fixture.
4 Likes
indeed. that one is good for both. mine isn’t digital. it is an old iron ballast with a capacitor for a hard start (like an AC unit). If i read correctly, it works for one bulb but not the other. That points at a bulb issue only to me.
2 Likes
you can put a switch on them and run both
could be 
a touch more information would help a bit
all the best
Dequilo
2 Likes
Could be issue with instant vs rapid start. There is an issue w not being interchangeable. Not an issue w the cord tho. It’s an issue between lamp and bulb. Happens semi-frequently in street lights and highbay shop lights. And yes comes from ~20 years commercial/ industrial electrical experience
3 Likes
Im out of date on HPS and MH tech. Its been a few decades since I messed with them, and havent kept up.
It sounded to me like both bulbs did work, but its unclear.
2 Likes
could be that indeed
had that problem with a brand of single ended bulb I liked
they changed from one to the other
my iron core ballast would not start the bulb all the time
sometime yes , sometimes no
talked with the vendor he told me they are one in the same
they are not
all the best
Dequilo
5 Likes
So I have a pic how my light socket comes of my ballast. Both of my ballasts are wired up the same on the outlet side. The cord in the pic will fire my 1 k hps on the 1k ballast but when I change the bulb and ballast to my 400 watt mh that outlet cord wont fire the 400 w mh bulb. It still works with second cord I have.
is the lamp cord that is not lighting your light longer then the
one that works?
may guess 
all the best
Dequilo
1 Like