Will not start, no lights, battery charged

It is hard to know what all is going on without seeing the truck and what has been modified over the years, so lets start with the starter relay. What are the exact symptoms? Do you hear a single, rather loud clunk from the starter solenoid each time you turn the ignition switch to "crank"? How about a light single click from the starter relay? Do you hear nothing at all? If so, what happens to the brightness of the head lights or interior light when you try to crank the engine? Have you tried shifting to "neutral" when cranking?

We will also want to know the exact battery voltage. It should read 12.6 volts if it is good and fully-charged. If that is what you find, a test light will work fine for the rest of the tests, but if you only have a digital voltmeter, that will be okay too.

I beg to differ. A majority of people do not realize there are at least three completely, totally different sets of symptoms that all fall under the general heading of "does not start". After rereading your original post, I should have assumed the starter was cranking the engine once you jump-started the battery, but I have sent many people down the wrong diagnostic path by assuming things. It is possible to have no lights, the engine will not run, but the starter does still crank the engine, which could have applied to your last sentence. That is why we need very precise symptoms.

This is perfect: "No lights no sound from the starter at all. Battery voltage is 12.7", and leaves nothing open to interpretation, ... Thank you. At this point I am going to shift gears and instead of a starter circuit problem, we need to look at what that has in common with the lights and everything else.

The online service information I have access to only goes back to 1982 models, which should be similar. When I head home, I am going to look at a diagram for my 1980 Volare which should be the same as for your truck. I am sorry that I might not have a better answer for you until tomorrow.

For now, put your meter's negative probe right on a paint-free point on the body instead of on the negative battery post. Go back to the starter relay and put the red lead on the red wire on that relay. You should still find twelve volts there. If you do not, follow the smaller negative battery wire to the body and see if that is corroded off. That is the ground return wire for all the lights and for everything on the truck except the starter and alternator.