Wiring problem.
89 Caprice station wagon - automatic - 307 engine

For the last few days I have had a problem.  Sometimes I turn on the
headlights and they dont work.  Othertimes they are fine.  But it's
not just the headlights.  The dome light, horn, clock, radio, power
windows, and other stuff dont work.  Yet, the engine starts and runs
fine.  The brake lights also work as well as the red lights on the
dash when I start the car, but not the lights that light up the dash.

I thought I may have had a bad ground.  I removed the ground wire from
the body (goes to the battery), and cleaned it.  I also cleaned the
battery terminals.  That did not solve it.

I have had a starting problem going on for several months, whereas the
starter did not engage in the flywheel every once and awhile.  I
decided that maybe the solenoid was not only the starting problem, but
possibly the reason for this "lights out" problem.  I got a new
starter and replaced it.  I cleaned all the wire terminals that go on
the starter before replacing them, and made sure the ends were not
loose on the wires.  After replacing the starter the lights worked
fine, so I thought I solved the problem.  Last evening I stopped in
town, and when I started the car, there were no lights again.  While
the car was sitting, the dome light, clock, etc. all came back on by
themselves.  As soon as I flipped on the headlight switch, the dome
light, clock etc. went dead again.  

I have confirmed that the ground is good to the car body, because to
get the car home (at night), I knew I had to somehow get headlights or
face the police, so I spliced a wire from the headlights supply wire,
directly to the battery.  (just the hot lead).  The lights worked
fine.  While driving home, suddenly all the things in the car started
to work again (horn, dash lights, clock, radio, etc).  

This really has me puzzled.........
What the heck could be causing this?
I downloaded a wiring diagram from autozone.  It shows several fusible
links.  But WHERE ARE THEY LOCATED?  Are they inside the harness?
I sort of thought that if a fusible link burns out, that's it.  Unless
somehow one of them is barely touching internally.  It;s bad enough
trying to trace something like this, but whenever I start to trace it,
the power comes back on again.  Talk about frustrating....

Anyone have a clue where those fusible links are?

***
One other thing.  There is a steel line that is connected to a vacuum
line on the top of the engine, drivers side / rear of engine.  It's
not connected to anything under the car.  I saw it when replacing the
starter.  It ends right near the exhaust pipe heat valve (that thing
that flips right under the ex-manifold.  Does anyone have any idea
what this line is for?  It's about a 3/16 dia. steel line with a
pointed end (below).

Thanks

George