First of all, thanks for the replies....

Art, I really don't know which of the ground wires is the one for the cluster.
There are either 5 or 6 of them that are all grounded to the metal frame of the center console, by a single screw. I don't know what any of them are for, or where they lead to.

I did notice that there is another ground at the transmission hump, just to the right of the accelerator pedal. I did not clean this ground but I think I'm going to go out and do so within the next day or two. Again, I don't know where that ground goes to but I'm honestly thinking about cleaning all of the grounds that I can find after seeing the results I got earlier.

I don't know if I mentioned it in my previous post, but cleaning these grounds did NOT make the tach start working. It solved a lot of other issues but not that one.

I was also very surprised that the warning lights started working because I was planning on getting under the car and cleaning the blue ground on the alternator. I didn't even know that wire existed until you told me about it when I was having some problems several years ago.
Having said that, the cleaning of the grounds and the alternator now functioning could be nothing more that coincidence. As I said in another post, the alternator would sometimes function and sometimes not function. I'm just wondering if there was some corrosion on the ground or the exciter wire that finally worked itself loose.

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I dream of a world where a chicken can cross the road without having its motives questioned.