Why is that doing this?
 

Basically give me the steps to diagnose these issues...please...

1991 N/A

No tachometer. When I got the car it would intermittently work...now it does nothing.

No speedometer. I tugged the cable at the connector and it did not pull through. I will be pulling the cluster and driving to see if it's spinning later.

Oil PSI gauge either does not work, or is very very slow. I'm going to check the contact momentarily.

To diagnose all I did check all the connections on the back of the cluster.

What dose work on it? Anything? For the tach check the trailing coil pack make sre it grounded tightly and the tach runs off the trailing coil. I think its a black wire i can not remembe, check page T-37 it starts with the wire diagram. pg T-38 has the spedo ect...

After a bad flood sometimes after removing the EGI fuse and cranking and replacing I would go to start and the fuse for the tach and gauge cluster would blow. This was a while back so I don't remember the frequency of this but every now and then IIRC.

Also, a noteworthy detail is that my speedometer would function normally in these conditions (blown fuse).

+1

Check the ground for the trailing coil, clean it sand it and coat the connection w/ dielectric grease.

It is very common for these oil pressure sending units to fail, wouldn't worry too much about that.

I was gonna say check your fuses for the Tach Speedo issue, For the Oil Pressure, who knows. I had a car with a bad cluster gauge one time. You have a spare cluster?

I have no spares.

I'll check the ground.

As far as what DOES work: The temp gauge seems to be working properly, the volt gauge works, and the fuel gauge seems to be going periodically.

Noteworthy perhaps, but completely coincidental.
Since the speedo is totally mechanical, fuses- blown or not- won't affect it at all, so don't let the speedo's actions warp your diagnosis of the other gauges performance.
You have two separate issues.

I did check the speedometer with a drill and it operated properly. It's not driving from the cable or the tranny one. Irritating....all the other gauges are optional but that one is required for inspection.

Plus, another quart of oil on the ground this morning...

Perhaps the speedo cable is broken.
If you disconnect it from the trans and put the drill on it, do you get anything on the speedo?
If not, then it's like $50 from the dealership, or was in 07 when I bought mine, or 65 from mazdatrix.

It's $19 from Advance/Autozone.

I've got bigger issues at the moment, though. No start...fuel pump not running. I have to take the multimeter out and play with it. Then I have to find out where the new oil is coming from. Then I can go back to worrying about the gauges.

I really wish they had something like a TrailTech Vapor for cars...

So I went out and hit the fuel pump with a hammer...bam, she works.

I need to know if there's a way to test the oil pressure sending unit for proper function...anyone know? It's a $50 part...don't want to drop $50 for something I don't need.

lets talk about what does work on the car

As said above...