[87Skier]

1 & 2 - look like starter. Some starters will have two wires. Tape up the one you don't use.

3 - Looks like HEI distributor connector

4 - I would guess A/C but I've never looked at A/C truck wiring

5 - Could be for electric choke. Looks similar to my 80's choke setup

6 - Temp gauge

7 - Fuel gauge?

8 - Brake valve

9 - unsure what the connector is for

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If you have a multimeter then set it to ohms on each auto or the lowest setting. You need to probe each end of the wire. Put one probe in at the main connector and the other at the other end of the wire.

It should read as less than 5 ohms, anything more indicates an issue.

You can do something similar with a test light by hooking up one end of the wire to the positive battery terminal, connecting the negative clip of the test light to the negative battery then probing the wire.

The downside is that test lights don't draw enough power to tell you if the wire will hold up to the rated current. A multimeter gives you a better indicator by telling you how much resistance is on the wire. More resistance means more your distributor, starter and AC compressor are getting less power than they should.

Besides doing a test fit there isn't anything more you need to test.