Ok, so I was able to tear into a few of my instrument clusters, in preparation for the 140mph speedo I just bought. In the process of doing this, I found some interesting differences. Now mind you, I don't know what year these clusters are, so I am taking a guess at what they came out of. If anyone can correct any mistakes I made with my assumptions, I'd love to hear it.

We will start with what I believe came in my 1985 GT, its the one on the bottom in the following picture, and it had an 85mph speedo that looks like the one above, but the tach only went to 6k rpms. So, are the blue bulb covers an indication of this being an 85 cluster?

The cluster on top shows red bulb covers, and a 7k rpm tach, so I am guessing this to be an 86 GT Speedo/Tach combination, is that a safe guess?

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My plan is to use the 7k rpm tach, and install the 140mph speedo alongside that, but I noticed that the cylinder selection knob is missing in this tach, so I was planning to just swap one from one of the other tachs I have... any reason this would be a bad idea? Better yet, any reason that the 7k tach wouldn't have this selection knob?

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Now moving on to another cluster that I thought was from an 84 or 85, as it looks like the one above with the 6k tach, and 85mph speedo, but has no bulb covers inside the housing. Maybe someone just removed them?

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Finally, I got into some early clusters, not sure which years, but since these all have green graphics on the gauges, I figure they are 1979 to 1983, right? After opening these up, I see that these all have blue bulb covers. I thought all of the early stuff had green lighting.... hmm. Anyway all of these gauges seem to be in good shape as well, and all of the tachs are set to V8 engines.

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So the final question of the day..... what color bulb covers do I run? Opinions? I honestly haven't seen what these look like at night, so I'm not sure which way to lean with this ever-so-important decision

Thanks again for all of the experience found in this site.