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I have two T12 Rapid Start ballasts for a two light fixture. I need to change out one ballast because of one ballast was bad. I bought a 1 or 2 bulb ballast and have wired up the bulb different ways but cannot get the second bulb to come on entirely. I have capped off my yellow wires and have used the blue and red wires to wire up the tombstones on my bulb. The bulb lights (barely) and flickers. Any advice on how to get this wired up correctly? The old ballast that was used before is no longer made. So, I crossed it to one that Grainger had said that I could use. Hmmm.

  • Can you post a photo of the wiring instructions on the ballast? – ThreePhaseEel Feb 24 '17 at 1:01
  • There is usually a diagram on the ballast follow that exactly if not correctly wired the ballast may be damaged. If you need to remove some of the wires from one of the tombstones a very small screwdriver or a striped piece of wire from the old ballast can be used to open the stab and remove the wire. Make sure a good connection is made with the new wire lightly pull back after inserting the stripped wire to make sure it locks. – Ed Beal Feb 24 '17 at 3:49
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    Was the ballast a rapid-start before? That is to say, were there 2 wires going to each end of each bulb? If it was previously 1 wire per end, that's an instant-start, and those usually use shorting tombstones. I get the impression you might be matching wire colors... and that will get you in trouble replacing an instant (red one end, blue the other) with a rapid (2 yellows one end, 2 blues or 2 reds the other end). – Harper Feb 25 '17 at 4:37
  • The ballast that I replaced was a magnetic rapid start series ballast for one bulb. It was a 120volt T 12 bulb ballast. The new one is an electronic rapid start ballast for either one or two bulbs. I hooked each red wire to each connector on the tombstone at one end then hooked each blue wire to the other end (the bulb has 2 connections at each end) then the hot and neutral wires were attached. I capped each yellow wire with a wire nut since I wasnt using them. I still cannot get the bulb to fully light when the switch is turned on. Any other advice would be greatly appreciated. – David G Feb 26 '17 at 5:57
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I'm a bit alarmed when I hear you say "capped off my yellow wires". A few ballasts do give that instruction, but not for 2-bulb use. I fear you might be matching up wire colors and not following the schematic on the ballast. Thing is, if the old ballast was instant-start, that will totally backfire. As you can see in these typical schematics, red and blue do quite different things on the two types of ballast. (ignore the LED one).

enter image description here

These schematics are not universal, only common. Yours is on the label on the ballast.

When converting instant-start to rapid-start, the other issue is shorting . The instant-starts only connect 1 wire to each end of the bulb, but it goes to both pins. This is almost always accomplished with a shorting lampholder (tombstone), which accepts one wire and connects it to both pins.

A shorting lampholder will have 2 holes for wires, but that's for daisy-chaining (as in the red wire above), not for 2 separate wires. A non-shorting lampholder intended for rapid-start ballasts will have 4 wire holes, 2 for each pin. The extras are for daisy-chaining, as in the yellow below.

Unless there's a visible wire to remove, there is no way to turn a shorting lampholder into a non-shorting one. You just need to buy replacements. They are fairly standardized, and I buy mine online for about 60 cents a tombstone. I buy only non-shorting types, it's easy enough to convert one into shorting with a wire.

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