Ok. Here's the results. I moved the starter relay ground to the engine ground under the alternator. I couldn't get to the ground on the right side rear of the engine, so I put it there. Here are the results.

Terminal 85 - 290mV when ignition in START
Terminal 86 - 31 ohms
Terminal 30 - 12.6V
Battery voltage applied to purple wire causes starter to turn

Sorry if this is short, but I'm doing this on my phone. ;-)

 

Terminal #86, (starter relay coil ground) resistance to ground measuring 31 ohms is too high for the relay to latch. Resistance needs to be less than 5 ohms. There's a poor/loose connection somewhere between the relay socket and engine ground. Trace the black wire from the socket to ground, or splice onto it near the fuse panel and run it to a good clean ground on the engine.

Terminal #85 comes from the P/N switch, (purple with white trace). The relay socket is not being supplied voltage in the START position. First check both terminals on the CRANK fuse, (fuse installed) when in the START position. Should show battery voltage on both fuse terminals. If not, the fuse is supplied voltage from the yellow wire at the ignition swtch, trace back and see if there's voltage at the ignition switch on the yellow wire.

EDIT: Terminals #30 & #87 are fine. There is no trigger or ground for the relay coil.

 

Well this just doesnt make any sense. The wire on terminal 86 goes to the A/C compressor clutch switch (the one that engages the clutch)???

 

Sounds like you're on the wrong relay. Clutch relay has a dark green and a dark green with white trace wires. Better double check.

EDIT: Starter relay is right next to the large fuses.

 

Nope, it was definitely the starter relay. Right next to where the large purple wire plugs in, and on the opposite side of the fuse box from The AC clutch relay. I also looked where the AC clutch relay is, but this black wire/white trace is definitely going from the starter relay to the ac clutch switch.

 

What color are all 4 of the wires in the starter relay socket?

What color are all 4 of the wires in the AC clutch relay socket?

 

On the starter relay, there's a small purple w/white trace, large purple, and a small black w/white trace.

I'm not exactly sure on the A/C relay--I've already put the truck back together because I was getting frustrated. I know I saw a green w/white trace on there, but that's all I can remember off hand. I'll go look later on.

 

Starter relay:
The large purple wire is good, (the starter engages when you apply battery voltage to it).
The purple w/white trace is there, but it's not receiving voltage from the P/N switch. That circuit needs to be traced back to find the problem. Most likely a broken wire or faulty P/N switch.
The black w/white trace wire needs to have less than 5 ohms to ground. The schematic shows that it's a black wire but color really doesn't matter, as long as it goes to ground. This wire needs to be traced to find the cause of the high resistance. Most likely a loose or poor connection.
The last terminal in the relay socket, (which is apparently vacant now) must receive battery voltage at all times. Again, it doesn't matter which fuse it comes from, as long as it's on the fused side of a 40 amp fuse, and has battery voltage at all times.

When all 3 of these problems are fixed, the starter will engage when you turn the ignition to the START position. Then we can move on to the fuel pump relay and figure out what its problem is

 

But my question is this: the black wire/white trace that currently goes from the starter relay to the A/C compressor clutch switch--where SHOULD it go?

I know the relay ground should go to ground, but right now it's connected to the A/C clutch switch. If I splice a ground in here, am I going to mess something up worse? Or do I need to pull the wire from where it is in the fuse box/relay now and plug it in somewhere else, and run a completely new wire from the starter relay to ground?

 

The concern right now is to get the starter relay working properly. We can deal with the dark green wires later.

The black w/white trace in the starter relay socket must go to ground, NOT to the compressor clutch relay. As you mentioned, you'll have to remove it from the AC relay socket and run it to ground to get the starter relay to work properly. Still need to get battery voltage to the socket as well. And figure out why the purple w/white trace doesn't get voltage.

Check the pins in the compressor clutch relay socket just so I have an idea what's going on there. Let me know what color wires are in there if they don't match up with this:
One pin should have battery voltage at all times.
One pin should have battery voltage in the START & RUN positions.
One pin should show less than 5 ohms resistance to the compressor clutch electrical connector when it's unplugged from the clutch, (dark green wire).
One pin gets ground from the PCM only when the PCM calls for compressor clutch engagment. (dark green w/white trace). At this point, we don't know if the AC works so it may be difficult to check the status of this wire.