On your tailgate issue clean everything you can reach with a toothbrush and some carb or electrical cleaner then use a graphite lubricant and they should work like new.

 

You can rewire the radio. There is a 95 service manual free to download (link at the beginning of the 1st gen forum). Ebay has a gagillion harness adapters in both male and female to update the colors to standard. They are usually about $4-$6 dollars. If you are not upgrading your head unit, and are not looking to amplify your speakers, you could buy the generic paper cone speakers and replace the existing ones (paper is better for low voltage sound as the paper is not as sensitive to frequency changes) at about $12 each (pepboys)

I live in Sarasota, so I know what you mean about the 10 months of heat.

The fan can be accessed by removing about 3-5 screws on the passenger side (without removing any dash parts). They do tend to collect hair, dust, and leaves. I cleaned a mouse nest out of mine. No filter that I know of.

I would guess that your headlight wiring was bypassed, or repaired at some point. The fact that your cluster is getting a signal is good, but the voltage is off, so the light is staying on. Typical of bulb sockets to collect moisture and corrode due to the galvanic effect.You can clean the contact area with a battery brush and add dielectric grease before installing the lamp bulb. Any wire that has been "tapped" should be repaired correctly. Pure black wires are typically ground for electronics (a common in homes for some reason), the black/yellow