Sir,
Sir,
Just got to approach this Lewis & Clark style. The longest journey starts with the first step & all that.
Listen, I'm serious when I say that 12 volt DC circuits are my favorite to troubleshoot. We aren't worried about
AC circuit impedance, frequency response, transmission line theory, standing waves, GHz waveguide magic, etc.
I happened across a short video that is so clear & concise about how to quantify the health of the
ground side of a 12v DC circuit.
I know that you are a well-adjusted, normal, non-sparky type, so don't tense up when this video starts. Just ride the wave,
this guy speaks in English not jibberish, the entire presentation builds to a logical conclusion, he proves his point using a very simple
example circuit, and if you can add this single skill to your electrical troubleshooting repertoire, *we* can get through this.
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In a
perfect world, not only do we replace, plugs, oil, filters, caps, rotors, tires, even paint, windshields, etc in order to keep our
GMT400s looking and running like new, we would also be able to completely yet easily replace the aging wiring harness too.
But this is the real world, so everyone in here reading this (as of this writing) gets to deal with a
22-36 year old wiring harness,
and replacing the entire wiring harness is a difficult, rare and notable event. And if I seem a bit pollyanna about all this, the last
dozen years of my military career I was doing the same thing for Block 25 & Block 32 F-16s back when they were showing
unmistakable signs of wiring harness aging.
When I left the computer room & rejoined the military right after 9/11, I was being asked by leadership why the Avionics package was
the LIMFAC to our fleet's reliability. I would take the officer out to the tail in question (see attached for an example) point out the year
it was made (2 digit numeral under the 'AF') and simply explain to them that because of the endless new tires, canopies, engines, paint,
etc., our planes did *look* new...but then I'd take them to anywhere there was wiring harness showing under an open panel (most places)
...and I would simply explain that nearly ALL of that wiring was installed that many years ago on the assembly line in Fort Worth, TX by
a company named General Dynamics.
Note: At the time the aircraft were also 20-somethings, and given the 9g loads and routinely being pushed as hard as possible, these
planes aged more like F1 cars instead of Nana's gently driven grocery getter. The officer would understand what we were up against.
In response to these concerns, we really put a lot of focus on tracking down and fixing non-black box intermittents reported by the
pilots in Debrief, instead of just waving them off as a MUC. (Momentary Undesirable Condition, a real thing at the end of some
troubleshooting flowcharts.) And with unrelenting focus in this area we were able over time to get our planes back to the way
they were when they were new. Black box go bad, we put known-good Black Box in, plane worky again. We wanted to remain a
manned fighter wing, instead of being moved to do a different mission, or worst-case being BRAC'd out of existence. So we were
highly motivated to make the very most of what we were given to work with. :0)
****
So apologies if my warped sense of humor made me color your perspective by referring to this area as a wiring diagram rainforest. I've
actually read elsewhere in this forum a talented member lead us all through a multifunction switch issue neatly. And if you were my pilot
and you mentioned any of the gauges in the cockpit moving when you did something else logically unrelated, that's where I'd ask you
if the suspect gauge just momentarily jump, or did it stay high -or- low until you ceased the (unrelated) input?
****
Of course the signals were more complex, but at the same time I was there, first-person, shoulder to shoulder with the users, other
flightline maintainers, and my own team. Here, we are all doing this remotely, relying upon the written word, pics, and sometimes
even video while using the FSMs. Personally, although the troubleshooting subject matter is something I got to do my entire military
& civilian career, at the same time I'm a newbie to the remote troubleshooting realm, and I'm still learning the ropes of how to do this
in such a way as to minimize the inevitable frustrations that come from not being able to see/touch/smell/etc the problem at hand.
And at the scene of the crime, most of us are working solo, which takes extra focus & patience to pull off this kind of thing.
And I never thought that I'd be doing this in public. But then again I never thought that even a vinyl-floored new chore truck would be so
far on the other side of $50K? And I've had to be careful with my own finances all my life, so I know what's it like to not have the option
of using the wallet wrench to get me out of a bind.
So here we are. As a motivated lurker I got way more than my fair share of hard-won info from this forum. And truth be told, I *still* enjoy a
challenging troubleshooting session and premeditated fix after all these years. And I decided that I had finally found a place where I
wanted to join the party already in progress. Especially with fellow GMT400 enthusiasts and straight up solid folks such as yourself.
So watch that video, maybe sleep on it, watch it again, and think about building up a little test circuit like he did in order to reinforce
what he was sharing...and if you have any questions, then I'll do my best to answer them.
Believe me, electrical gremlins used to ground airplanes and also keep me from driving a new (to me) well-used vehicle no further away from
my abode than I was willing to walk back home if need be. But being able to take something like an old Fiat Spider halfway across country
in order to attend some mandatory 7-level training was a hoot.
Apologies for the length. I'm hoping that between the all of us we can figure out the answer to your simple question about how
your foot on the brake pedal disturbs the fuel quantity reported by the gas gauge. :0)
Because if we can do that, then we will have honed our skills for sorting out other aging GMT400 wiring harness issues. And being able
to drive our old GMT400s without constant worrying about the electrical system failing us is a worthwhile goal.
Cheers --
PS -
F-16 Wiki article.