By buying the parts unassembled, you can probably construct a light for half of what it would cost "ready made" from a hydro shop. Many people might be reluctant to work with wires and electricity, which is certainly understandable, But it isn't nearly as difficult as you might think.
Let's examine what is inside a ballast. An high pressure sodium (HPS) ballast consists of 3 parts: The transformer, the capacitor, and the ignitor. A metal halide (MH) ballast generally has just the transformer and capacitor.
Look in the yellow pages under "lighting". Call them and ask if they carry "Transformer, capacitor, ignitor (if for HPS), and socket" for whatever size bulb you wish to use (150, 400, 1000 etc.) and type (MH or HPS) light you wish to purchase. Odds are they will have it. You can also order this stuff from many online electrical supply places.
When you purchase your ballast components, be sure to buy the correct line voltage rating you intend to operate it on. Most homes in the US are wired for 120 volts. If your house happens to have a different voltage (IE: 210) then you need the corresponding ballast parts.
Another option is to purchase what is known as a "multi-tap" ballast. This type of ballast has a wire connection can be changed to allow several optional voltages. Some stores may only carry multi-tap ballasts to save money on inventory. A multi-tap ballast will work fine in any situation. Multi-tap ballasts usually have the following options inside: 120/208/240 and 277 volts.
Besides the transformer, ignitor, capacitor, bulb and socket, you are going to also need the following: About 20 feet of 14 (or better) gauge wire, a male plug set, about 8 wire nuts.
The wire and plug are for installing the power cord and socket to your ballast. You can also buy a long heavy duty extension cord, which you then will cut up. Whatever wire you buy, make sure it is rated to at least 15 amps and 1500 watts (14 gauge). That size is good for wiring all the way up to 1000W lights.
When you get your parts, you will also get a wiring diagram. It may come on a separate sheet of paper or it will be on a label on the transformer.
I have added a few descriptions for the sake of clarity, but the basic schematic is the same. This is for a HPS lamp and describes the wiring for the 3 internal components and socket. For some people, the schematic may be a little confusing.
If you look at the transformer, you can see it is labeled as having a "short side" and a "Long side". These are my descriptions for the two different areas of the transformer. If you look carefully you will see that the transformer has two protuberances where wires come out. One of them is thicker than the other. That is the "long side". It is important to know the difference when you’re wiring it. The capacitor is a simple affair with just 2 wires.
The ignitor has 3 wires. Look closely at the wires running from the socket. You can see that each of them comes to a junction with 2 other wires. All 3 wires at a junction (and at all junction points for all wires) are held together using a "wire nut". This is just a plastic cap which screws onto wires to hold them together. Make all the wire connections using wire nuts, do not use tape.
All wires have something printed on them so you can identify them. It is going to be something numerical("X1","120") or alphabetical ("lamp", "com"). In my example, wires are noted with X1 or X2 or X3, other ballast kits may have wires which simply say "one" or "Two" and "volts"(instead of "120"). Sometimes wires are colored (the ignitor wires in my example are red blue and white) sometimes not. When wiring a ballast, don't get mislead by the color of wires on the ignitor, capacitor or transformer. These wires are connected according to what is written on them, not by color. Color will only come into play when dealing with wires coming from your power cord and socket. These are going to simply be black, white and green with no labeling.
HPS
This wiring description is for an advance brand ballast. If you end up with a different brand and the wiring doesn't seem quite the same, then it isn't. But should not be very difficult to figure out the difference after familiarizing yourself with the various wires and parts in the illustrations.
First, orient the transformer so that you know which side is "long" and which is "short". Locate the 2 wires that say "cap" on them. They should be coming from the inside of the transformer bulges. These wires all either get connected directly to the capacitor using connectors or by soldering, or with wire nuts to the wires coming from the capacitor.
Next, locate the wire coming from the long side of the transformer which is labeled somewhere with the number 3 (or "X3"). Then with a wire nut, connect it to the number 3 wire coming from the ignitor. Make sure the nut goes down snugly and that no bare wire can be seen.
Before going any further, you need to figure out how far from the ballast the bulb will be placed. Usually the wires will usually be 6 to 10 feet long. Use a piece of heavy duty (extension cord) wire and wire nuts to extend the socket's wires as far as you need to. Just attach black to black, and white to white. The green wire is a ground which will get attached to your reflector on one end, and to the transformer base/ballast box on the other end to safeguard against shock.
Then, find the white wire labeled "com X2" (or "com2" or whatever it is in your particular case) coming from the transformer's short side, the #2 wire from the ignitor (it may also say "com X2" or "com2" or simply "2"), and the white wire from the socket. Connect all 3 of these wires together using a wire nut. Make sure the connection is tight with no bare wire showing.
Find the wire coming from the transformer's long side labeled "lamp". Along with the #1 ("X1" or "1") wire from the ignitor and the black wire from the socket. As above, connect all 3 wires together with a wire nut.
The last 2 wires should come from the transformer's short side. One should say "com" and the other "120". These are the two wires that will go to your power cord. Cut the extension cord to the right size and trim away the outer insulation to expose the 3 wires (white, black and green).
The white wire gets connected to the "com" wire on the transformer, while the black wire goes with the "120" (or whichever voltage you have) on the transformer. The green wire is the ground and that gets attached to either the ballast box or the base of the transformer to safeguard against shock.
Now for multi-tap ballasts. There should be a wire with a connector clip on it attached to 1 of 4 possible spots on the transformer. These 4 options are for 4 different voltages. Find the one labeled "120" (or whatever your voltage is) and attach the wire/clip to that one. Some ballasts simply have a few extra wires inside labeled for different voltages. In that case, find the one for your voltage and strip the insulation off the end, then connect it with a wire nut to the black from the power cord. Make sure to leave the other voltage wires with all their insulation. For safety's sake, cover each of the unused wires (individually) using a spare wire nut for each one to insulate them.
MH
If you want a metal halide light, your task is even easier because now you only have the transformer and capacitor to work with and no ignitor. This is for standard metal halide ballasts. On occasion, you run into a MH ballast which has an ignitor. Try not to get this kind if you can. If this is the only option, then follow the instructions for HPS ballasts.
Connect the wire labeled "cap" coming from the transformer's long side to the capacitor. Connect the other wire coming from the capacitor (labeled "lamp") to the black socket wire.
The transformers short side will either have 1 or 2 wires coming from it labeled "com". If there is only one, then connect that wire with both the socket's white wire and the power cord's white wire. If there are 2 "com" wires, then pick one and connect it to the socket's white wire. Then connect the other "com" wire to the power cord's white wire. Connect the power cord's black wire to the transformer's short side wire labeled "volts" or "120" (or whatever voltage you have).
Testing
Now, even though it will work without it, I recommend grounding the socket and power cords. The grounds are the green wires coming from these 2 cords. Both of these wires should be attached either to the metal base of the transformer or to the inside of the ballast box if it is made of metal. The other end of the socket ground gets attached to the metal part of the reflector. Double check everything. Screw the bulb in the socket, then plug in the power cord. The ballast should hum and the bulb should come on almost immediately. If it doesn't or if you see or hear anything unusual, unplug it.
Most likely, if you made a mistake, then the bulb simply will not light. Always wait five to ten minutes before touching any of the wires after unplugging the unit. This is because the capacitor holds electricity and you may get shocked if you touch the wrong wire. Double check everything again.
A quick word about the bulbs. While all HPS bulbs can burn in any position, a MH bulb must be purchased specific to the mounting position you intend to use. There are MH bulbs made specifically for horizontal placement, base-up placement, vertical (base down) placement and also universal placement. The universal type bulbs can burn in any position, but are not quite as bright (maybe 5% less) as the position specific bulbs.
