I finished up the swap over the weekend so I figured I'd post a little more about how to get the separate oil & volt cluster up & working. I started with this diagram which lets you know what it would tie into if it had been wired for it from the factory.
So you look at what each wire in the gauges does and find the number on the diagram. I then cut the plugs off & labled the wires. Some on the voltmeter were a different color than the diagram said, but they were in the right location in the plug, so it worked out.
Looking at the diagram, you can see that the oil & volt gauge ties into the main cluster. It shows which wires on the separate gauge connect to which wires on the main gauge. Here's what I came up with:
19 & 21(oil) -----> 17
18 & 22---------->6
21(volt) & 23----->12
24---------------> Oil sending unit
Notice there is a 21 on each gauge for some reason.
Splicing into main cluster wires
And connecting those to the new cluster (I used 16 gauge wire)
I need to pull the piece that actually connects the wire to the oil sending unit from a junkyard. I just wrapped the wire around the connection on the sending unit which will work for now, but I should do it right. I'll just get someone to cut the connector off a dead truck, and I'll splice it into mine. It all works! I've got illumination and volt & oil pressure readings now finally.