I have an old ballast gone bad in and 8ft t12 fixture. I have a replacement ballast but it is a single pin bulb. The old ballast has 1 red 1 blue 1 black and 1 white new ballast has 2 red 2 blue 2 yellow and power black and white and I’m stuck on how to convert the old to the new. Diagram says it runs a 2/96t12 fixture
I can't tell you what you should do but I can tell you what I have done over the past 15 years. First let me say that T12 technology is highly inefficient and new T8 and T5 with electronic ballasts are 33% more efficient and lets not forget LED technology. Also, if you haven't noticed, manufacturers are slowly eliminating T12 parts.
So I always do a total retrofit of the entire fixture. Starting with replacing the tombstones, and finishing with the new disconnects at the power source. It not only prevents confusion of how to replace the existing wiring (just follow the diagram on the new ballast or driver), but it eliminates all of the wire nut splices inside the fixture, which can always create problems. Many people think this is more complicated to do this, but we adapted it because it was simpler, easier to install, and took less time with fewer problems and mistakes. Even though this may not matter to a DIYer, it eliminated many warranty calls and dissatisfied customers.
You can find multiple retrofit packages to select from online.
Hope this helps and good luck.
8-foot fluorescents are different
The standard 8' fluorescent tube (70W, F96T12) has 1 pin on each end, a little nub. * There also exist 2-pin tubes in HO (110W) and VHO (210W), but you don't have that. **
I'm guessing that your fixture has 1 tube in it, since your old ballast has only 1 blue and 1 red wire.
The new ballast you have is definitely wrong for your fixture. It can only work on tubes with 2 pins per bulb end - either HO/VHO tubes (as said, you don't have that) or common 4' tubes. Read the label and it will say.
The ballast you actually need (96", 1-lamp, F96T12, instant-start) has been replaced by 2-lamp ballasts that also work with 1-lamp. You need to read their data sheet and make sure they specify 1 or 2 lamps. The ballast will have a spare wire that you won't use; cap that off and wrap it liberally with electrical tape as it will have 1000V on it. Don't snip it off (you can't cap it then), just coil it up, in case you ever want to reuse it on a 2-lamp fixture.
This will be an electronic ballast, which will be much more efficient. (they also stopped making ballasts in 120, 208, 240 and 277V; now one ballast works on all voltages.)
You can gain some more efficiency going to T8 tubes and getting a different T8 ballast. These are the smaller diameter tubes, same size and nub, will fit. You must use T8 bulbs with T8 ballasts, or T12 bulbs with T12 ballasts! They will cross-fit, but they won't work.
If you want, you can convert the fixture to LED "tubes", in which case you will not use any ballast at all. (use a direct-wire type LED). Some people are big fans of this. I don't trust cheap LED's build quality.
* The fluorescent technology geek will note that "1 wire per lamp end" absolutely requires an "instant start" configuration, where the arc is struck with a huge spike of voltage on a cold lamp. This is harder on the tube, but 8' tubes are built for this punishment. This choice is made for you. ** The fluorescent geek will note this mandates rapid/programmed-start, in which each bulb end is preheated before the arc is struck. Here again the choice is made for you; these tubes are too high-performance and too delicate to cold-start, preheat is mandatory.