OK, got a few minutes now.
Long post, but I tried to throw everything in at once so you can do a lot of stuff before you have to stop and ask questions.
Read the whole thing, and see what part is best for your situation.
Also, post the particulars of the truck so we can know which schematics and stuff applies.
First, we need to make sure you have a drain. Check the battery voltage with the truck off.
If its 11.5 or less, then its badly discharged, and it needs to be charged before we can do much.
A battery charger is best, although you can crank the truck and let it run.
Alternators are not the best for charging a dead battery, but if thats all you got then thats what we use.
When you get the truck running, measure the voltage at the battery with everything else turned off.
Fan, lights, that sort of thing.
It should be 14.5 volts, but if the battery is almost dead, it might be as low as 13.5 and still be OK.
After it has run for a while if it doesn't get close to 14.5 at fast idle, then you probably either have a bad battery, loose connections somewhere, or an alternator problem.
Once we get the battery voltage up to where is should be, take the negative battery cable off, and hook the meter between the negative post and the cable with it set on volts, not amps.
We don't want to risk blowing the fuse in the meter right now.
You should see full battery voltage. If not, then you do not have a drain, and you need to check the battery. It may have an internal short.
If you have full battery voltage, then you need to start pulling fuses.
First, look around carefully and make sure you have left something on by mistake. Dome light, things like that.
As for pulling the fuses, there are two methods I have seen used.
Some people pull them all and then put them back one at a time.
Others pull them one at a time.
You may have more than one drain.
If you have a computer in the car, then it will have a drain all the time. Some radios do too.
Using the meter in volts mode will show those all the time even though they are normal.
I would pull the fuses one at a time until I saw a drop on the meter.
Then see what you pulled.
If you have a computer, pull that fuse first so that it does not give a false positive.
If you don't find a really good reaction that way, then you will have go to current mode.
If your meter has a 20 amp fused current input, you can try this first if you want to.
If you have a test light, put it between the post and cable instead of the meter. If its good and bright, pull fuses until it dims.
Or put the meter on 20 amps and make sure to use the 20 amp input.
Put it between the post and cable and read the amps.
With no computer and no radio, and everything turned off, you should read in the low milliamp range.
There is usually enough leakage to show up a tiny amount.
If its higher, in the 500ma range or more, then start pulling fuses until it goes away.
If it does not go away pulling fuses one at a time, then you will have to pull them all until you find the two or three that have the drain.
If you pull them all and still have a drain, then you need to trace the wires from the battery to the starter, to the fuse links.
Take the negative wire loose, and then take the fuse links off the starter and then hook the meter back up and hook up the fuse links one or the other until you figure out what link powers the short.
And trace it from there.
I suspect that you will find it fairly quickly with the fuse pulling. After you find out which fuse, then we can try to run it down further.
One trick I have used in the past, was to take a good closeup picture of the fuse box with a digital camera.
The fuses are color coded, and a good color picture makes putting them back in the right places a lot faster than reading the labels.
Also, since some of the slots are not used, this shows them too.
If you have a small laptop, a smart phone, or even a smart picture frame, you can view the .jpg while you work.
Otherwise, you can get the picture printed out at several shops cheap.
I had pulled fuses and the draw was still there no matter what I pulled and I didn't know where to go from there. 
Thanks much. I have a little time tomorrow to do some checking. I will post back up when I have something one way or another. Again, thanks for the help.
