OK, I know another thing that could be the root of the problem. Bear with me here. If you look at a GM wiring diagram in Mitchel's, trace the orange
wires, you will see that all power supply wires are in fact orange, or orange/black stripe, and all come together at a common point. This point is
under the dash and carpet,
and takes more than a few hours to fix. First, find the wire bundle and trace it until you find the point where they
all come together. Un-ape the wires as you go. You will see, when accessed, that at least 11 power supply wires come together, with no fuse of breaker
of any kind. Usually there are 5 on one side, 6 on the other, more accessories means more wires. This is General Motors built in obsolesces. Say that
that little switch on the door that turns on the interior light get wet and shorts. This one short is far reaching. Voltage drops.Things began to go
wrong, Engine refuses to start, then starts later. Light are dimmed, or flashing.
What we do is buy one
50 Amp automotive circuit breaker
from an auto parts store. Cut the wires, and, and
place a ring type terminal on each wire, keeping then separate, some on one side, some on the other side. Place the rings on the breaker, tighten the
nuts, and tape it up real good. Put the dash back in, and screw everything down tight.
You will notice a vast improvement right away. More power is available, lights are much brighter, every electrical device works better.
For a good wrench this is a 2 & 1/2 hour job. And it is worth the effort. We charge $250 to do this, and every time it is very successful. Try it if
you dare, and good luck to you. Once learned, you can make money off off your friends fixing their GM cars and trucks. Every GM since 1986 had this
built in problem. Fords and Dodges are different, I am GM trained.