My headlights do take a couple of seconds to come on after pressing the switch and the dash lights take a few more seconds to come on after the headlights do.
That's an interesting observation. In electronics, in order to set up timing
circuits we will on purpose vary the relationship between the Resistance and
Capacitance so that we can achieve whatever frequency is needed. In these
conversations the phrase 'RC Time Constant' is overheard.
(
RC Time Constant)
...but I digress. The point is that the lighting circuits you are powering
have a certain amount of natural stray capacitance from Day 1, which is normally
a don't care bit of trivia. But if there's increasing Resistance to current flow
feeding this circuit, then it seems that between Mother Nature and Father Time
we now have a homegrown 'RC Network' that is causing the power applied to
ramp up slowly (instead of immediately) ...giving you the symptoms that
you are observing?
Hang in there, I'm going somewhere with all this. Earlier you mentioned
that you have already cleaned up all the 'engine grounds'. That's good news.
But the exterior lighting circuit does *not* rely upon the engine grounds.
(Or the G202 described in my earlier reply.) Instead, on the GMT400s there
are not 1 but 2 "sheet metal grounds" on the radiator support. 1 on each side,
close to each headlight, and they support the current flow for the headlights,
turn signals, horn, etc.
Here's the ground distribution circuit for the exterior lighting:
You must be registered for see images attach
Although the fuel pump is your primary focus right now, as soon as you get that issue
sorted out, I'd like you to find G104 & G105 and make them as good as new again.
And in order to provide a solid current return path for G104 & G105 on the radiator support,
you should also perfect the condition of G101 near the battery. IF you do all this and it still takes
noticeable time for the voltage to rise high enough to make your headlights come on normally,
then we need to take a look at the power side of things. (In my following reply.)
****
Why the flood of info on your truck's electrical system? Well, in reply #14 above you
described how much money you've paid others to do their job & they came up short,
and that sux. So if we can pool all our knowledge & experience in order to get all the
electrical gremlins tracked down & eliminated, then all this can be charged to the
School of Hard Knocks tuition column instead of just writing off the whole shebang as
a lost cause. (And also help others reading along researching similar issues can follow
your lead towards a successful resolution.)
Keep fighting the good fight. Looking forward to your status updates.
Cheers --