96 GMC K2500 Suburban Restoration (with a couple of mods)

[Erik the Awful]

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Dang 'ol pointy head avionics troops. As a former AGE technician, I can confidently say you're overthinking it.

Here's the best bang for your buck on a meter.
www.amazon.com/Fluke-101-Multimeter-Resistance-Capacitance/dp/B00HE6MIJY/

Get a test light also.
www.amazon.com/Automotive-Circuit-Material-Alligator-Continuity/dp/B0928XB89R/

I can probably count on one hand the number of times I've done ohms checks on 12v powered equipment. Meanwhile the pointy heads were "shooting wires" on the aircraft almost every day. Your truck does not have a high powered radar or UHF. Keep it simple. Make sure your grounds are tight and clean. If a wire's growing corrosion, cut it back, splice it once, or replace it.

Yes, at low voltages it's hard for a consumer grade meter to discern between 0.0 and 0.2 ohms. That's why I don't shoot wires. Watch that TPS voltage instead. It should be near zero at rest, run smoothly up to 4.5 or so, and then return smoothly. If you have that, it's fine.

 

[Road Trip]

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Dang 'ol pointy head avionics troops. As a former AGE technician, I can confidently say you're overthinking it.

LOL - you brought back some fond memories of what it was like
to be the geek that others would flee when we started talking about
our stuff.

Seriously, when someone first starts out in electrical troubleshooting
they really rely on what the meter tells them. But as they build experience,
they discover that by using their other senses at the same time allows
them to troubleshoot while using the meter less for actual troubleshooting
and more for just pre/post verification.

****

Here's a quick example. I was asked to troubleshoot the hard starting
of a '70 Chevelle with a high-compression 383ci SBC. It was a slow cranking
issue that had resisted repair by others. Battery had been upgraded
to a stout one with 800 cold cranking amps. Battery was fully charged,
and passed a load test easily.

Car would barely start cold, and when it was hot it wouldn't turn over
fast enough to start, so the owner would be forced to open the hood
and wait for the engine bay to cool before he could go home.

All relevant connections were clean & tight, and would have passed
any resistance check I might have made. The starter sounded healthy
& shimmed up correctly, just too slow. I knew that a lot of current
was being drawn, for if you watched the positive cable down to the
starter it would jump ever so slightly when the key was turned to
start. (!)

The problem? The best we could tell, that '70 Chevelle had a low
compression 307-2bbl when originally built. Both positive & negative
battery cables were original, in good condition, but were sized like
something you would expect to see on a straight 6?

I told the owner that we needed to upgrade the battery cables
to better match the requirements of the high compression
383. I recommended that whatever GM did for the LS5 454 equipped
'70 Chevelles would be the place to start.

That's what we did. He actually got the cables listed for the big block,
and they were indeed much heftier. And from the first start with the
new cables we knew we had a solid fix! Worked as advertised, hot or
cold.

And I didn't use a meter for any of this. After decades of intently
watching all manner of SBC & BBC engines start, you just see
the patterns & react at a near muscle memory level. And if I had
to guess, Erik I bet you worked in a similar fashion on your AGE.
We start out using our written guidance like a cookbook, step by
step, hoping like hell that we were being led to a successful resolution.

But after enough time in the kitchen, while the book may still be
open, my nose is now guiding me through the process. (Yup,
this stew now smells the same way that it did the last time, and that
was a crowd pleaser!)

****

Actually, my goal was not to try to get the OP to break the piggy
bank & fill a cabinet with specialized test equipment. Instead, I
just wanted him to know that if he was getting squirrelly readings,
it wasn't his fault so much as the limitations of all handheld multimeters.

And that it *is* possible to quantify very small amounts of circuit
resistance in milliohms reliably. (or large amounts of conductance in mhos,
take your pick.)

But with a little experience, if he chooses to, someday he will simply
stand by the front fender helping a friend or neighbor troubleshoot,
listen to the motor crank over, see the too-small cable, and know
that it isn't up to the job.

And the whole time there won't be a meter in sight. :0)

 

[Road Trip]

Here's the best bang for your buck on a meter.
www.amazon.com/Fluke-101-Multimeter-Resistance-Capacitance/dp/B00HE6MIJY/

Get a test light also.
www.amazon.com/Automotive-Circuit-Material-Alligator-Continuity/dp/B0928XB89R/

I can probably count on one hand the number of times I've done ohms checks on 12v powered equipment. Meanwhile the pointy heads were "shooting wires" on the aircraft almost every day. Your truck does not have a high powered radar or UHF. Keep it simple. Make sure your grounds are tight and clean. If a wire's growing corrosion, cut it back, splice it once, or replace it.

Sage advice. And if you know the limits of your test equipment, you will know when
it's best to measure and when it's best to go with your gut feel. Good stuff!

Yes, at low voltages it's hard for a consumer grade meter to discern between 0.0 and 0.2 ohms. That's why I don't shoot wires. Watch that TPS voltage instead. It should be near zero at rest, run smoothly up to 4.5 or so, and then return smoothly. If you have that, it's fine.

Agreed. I'm with you, the actual signal is of more interest to me. The
ohmmeter only comes out when standard broke/fix methods (what you
outlined above) don't deliver the fix.

Although it's hard to tell from my typing, I'm actually a big proponent
of a 'measured response' to any repair scenario. If all we have is a leaky
valve cover, then I'm not the one trying to sell a complete engine swap. :0)

But at the same time I won't hesitate to drag out whatever is necessary in
order to either measure the signal, or even see the signal so that I can
evaluate the signal/noise ratio. For example, I was helping a good friend
with setting up a knock sensor where there originally there wasn't one.

And since our goal was to run ~2 atmospheres of intercooled boost
through the motor, protecting this assembly with a knock sensor
was literally a make or break safety circuit. So, in order to really
know if this new (unknown) sensor was working properly, I
decided to test it this a way: (Turn the sound low first)

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That's my trusty old analog Tektronix 475 oscilloscope showing
how the piezo-based knock sensor can actually make a voltage
into a high impedance circuit like an o-scope. It also shows
that every engine block rings like a bell, even when fully assembled.
(Each block design {SBC, BBC, SBF, etc} has it's own resonant
frequency, and in order to improve the signal/noise ratio, often
the knock sensor will be fine tuned to match.)

The good news is that the knock sensor circuit worked! But
I just want to assure Erik that before I drag out the scope I
will first try the multimeter. And before I drag out the multimeter
I use common sense (cleaning, tightening, etc) to see if
I can Fix Machine, Get Banana.

To me, a measured response is the way to go. Fun, too!

Sincerely,

Your flightline Nerd
(Same as it ever was)

 

[South VA]

****

I sincerely apologize for the length, but after all this if I ask you
to get as close to 0.0 ohms as you can on any high current
connection in our limited 12-volt world, I am serious about that...
for I don't want your gf to want you to get rid of your GMT400 and
get into something newer. (Heck, plenty of newer stuff breaks
too! :0)

Remember, keep the mission-critical circuits in new condition &
you will gain the reliability AND lose the fear of the aging
wiring harness.

Enjoy your upcoming adventure --

No worries about the lengthy post @Road Trip. I very much appreciate what you've shared.

I like the divide & conquer approach. It makes a lot of sense. However, as you pointed out, "...of course if the vehicle sat & critters started chewing the wires then a full harness visual inspection is your only recourse."

Since this Burb sat for I don't know how long, and had the aforementioned packrat firmly ensconced under the hood for long enough to fully furnish the space (I really need to ask the PO if he has a picture), I'm right there.

So my approach has pretty much just that: to inspect everything I can get to, visually and by touch. There were a few places where the split wire loom was chewed through, but the wire insulation was left unmolested. Mostly. The major exception was the battery to engine ground cable, which had a lot of insulation removed, and the wire strands had begun to separate. Coupled with the marginal battery to body ground, I'm thinking this is where most of the charging system problems originated.

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Fortunately, I suppose in part due to this thing having virtually no rust, all of my ground straps seem to be intact and in good shape.

The hot leads appear to be intact, or have been replaced.

Lest I forget, thanks to the timely suggestion by @tayto, the Burb is sporting a brand new ignition switch. Apparently a bad switch can cause some of the very symptoms it was experiencing, particularly intermittent transmission shifting issues.

My hypothesis is that the ground wiring contributed to the charging system issues, and the ignition switch affected the transmission shifting. Crazy, but that's what the evidence suggests, at least so far. Looking back, the alternator that was replaced during our second camping trip may or may not have needed to be replaced. I don't know. Ah well.

To @Road Trip and @Erik the Awful, I bought this Klein a few months back to use in the house renovation I'm working on. It seemed to be a reasonable step up from the really cheap one I owned and subsequently blew up. It's what I've been using for working on the Burb.

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Not to digress (but I will), here's the back of the existing panel in said house, an FHA manufactured home built in the 70s. I'd like to think that some nonelectrician 'upgraded' the panel during a remodel, rather than it being sent this way from the factory.

Why it hasn't burned down is beyond me.

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I'm fortunate to know an electrician who is willing to pull the permit and act mainly as a consultant, answering my questions and inspecting my work before the formal County inspections. I've done this a couple of times in the past, in other houses, and it worked out well. This Klein 420 is probably ok for that task, but may not be sensitive enough for automotive work.

In any case, I am really hesitant about spending $450 on the Fluke, and building one myself is beyond my skill set, much less my comprehension. The milliohmmeter you suggested may be the best bet for my increasingly stretched tool and parts budget. However, for now I'm going to stick with the DMM I have, and focus on checking connections and wire integrity. I also own a test light, but haven't used it in quite some time. Maybe time to bring it out of retirement.

Again, thanks @Road Trip and @Erik the Awful and @HotWheelsBurban and @GrimsterGMC and @Orpedcrow for taking enough of an interest to read this thread and share what you know. Thanks to your advice and encouragement I'm feeling a whole lot better about this vehicle than I did a month or so back. I seem to be rapidly losing my nearly superstitious dread of what might happen next.

Oh, and recently my gf had the nerve to refer to the Burb as a "money pit!"

I informed her that most of my expenditures have actually been comparatively modest. Numerous, admittedly, but modest.

She laughed.

 

[Road Trip]

Not to digress (but I will), here's the back of the existing panel in said house, an FHA manufactured home built in the 70s. I'd like to think that some nonelectrician 'upgraded' the panel during a remodel, rather than it being sent this way from the factory.

Why it hasn't burned down is beyond me.

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Yikes! Fixing that *is* a priority. One of those things where life
inserts stuff like this when you would really rather be doing the 'burban thing!

This Klein 420 is probably ok for that task, but may not be sensitive enough for automotive work.

In any case, I am really hesitant about spending $450 on the Fluke, and building one myself is beyond my skill set, much less my comprehension. The milliohmmeter you suggested may be the best bet for my increasingly stretched tool and parts budget. However, for now I'm going to stick with the DMM I have, and focus on checking connections and wire integrity. I also own a test light, but haven't used it in quite some time. Maybe time to bring it out of retirement.

I actually think that by upgrading to the Klein from what we all started out
with is going to do the trick for you. Glad to see that you are working
with something rugged enough that it will stand up to being used in anger
on a vehicle.

As for big dollar Fluke, no need at all unless your Klein gives up on you.
(And there's a 99.99% chance that the Klein will outlast both of us
- just don't leave the battery in it during extended periods of non-use.)

As Erik pointed out, the entry level Fluke is more than good enough for
what we're trying to accomplish.

In reality, the pro Fluke AND the milliohmmeter should just be kept in the
back of the mind, not to purchase, but just take comfort in the fact that
we can always bring more to bear IF we choose to. Just knowing that
if my plan A for electrical troubleshooting doesn't work, then there's a
Plan B, or even Plan C waiting in the wings always gives me confidence.

Shoot, between your clear photos, your Klein, your never say die attitude,
+ a few characters looking over your shoulder here on the forum, I have
confidence that you will bring you 'burban as far as you wish to take it.

 

[Orpedcrow]

Having owned and used the same multimeter that I was provided with at tech school 15 years ago, I’ve learned to change the battery more often than probably necessary due to funky readings and misdiagnosed electrical towards the end of the 9v batteries life.

Another thing I was taught long ago is to “zero out” the meter when checking resistance. This is a super complicated and detailed procedure so screen shot and print it out if necessary.

Turn the meter to ohms, touch your leads together.

That will give you a baseline reading of the resistance (if any) of your leads that you can subtract from what you’re actually measuring.

 

[termite]

Having owned and used the same multimeter that I was provided with at tech school 15 years ago, I’ve learned to change the battery more often than probably necessary due to funky readings and misdiagnosed electrical towards the end of the 9v batteries life.

Another thing I was taught long ago is to “zero out” the meter when checking resistance. This is a super complicated and detailed procedure so screen shot and print it out if necessary.

Turn the meter to ohms, touch your leads together.

That will give you a baseline reading of the resistance (if any) of your leads that you can subtract from what you’re actually measuring.

This has lead me to replace three different meters over approximately 15 years. Two craftsman and one fluke. Wasn't able to get a set of leads easily when needed for the fluke and both craftsman meters wouldn't give reliable zero readings. Guessing broken wires in leads or inside the case.

 

[South VA]

Having owned and used the same multimeter that I was provided with at tech school 15 years ago, I’ve learned to change the battery more often than probably necessary due to funky readings and misdiagnosed electrical towards the end of the 9v batteries life.

Another thing I was taught long ago is to “zero out” the meter when checking resistance. This is a super complicated and detailed procedure so screen shot and print it out if necessary.

Turn the meter to ohms, touch your leads together.

That will give you a baseline reading of the resistance (if any) of your leads that you can subtract from what you’re actually measuring.

Duly noted - thanks!

Another 113 miles of mixed driving today.

It turns out that the voltage gauge does in fact move, very slightly, with the turn indicator. I’m not sure if it’s a concern. I seem to remember reading that it’s not uncommon in many vehicles. Thoughts, anyone?

The indicated voltage stayed between 13 ¾ and 14+. The needle was at least touching the 14 mark the whole way.

The transmission shifted without drama. There were no harsh shifts, and no being stuck in gear. I would have expected at least the harsh shifts to have shown up by now, if they were going to show at all.

I’m going for one more test drive tomorrow, just to be sure. If it’s similarly uneventful, I’ll feel like the Burb’s ready to make the trip on Monday.

 

[HotWheelsBurban]

Duly noted - thanks!

Another 113 miles of mixed driving today.

It turns out that the voltage gauge does in fact move, very slightly, with the turn indicator. I’m not sure if it’s a concern. I seem to remember reading that it’s not uncommon in many vehicles. Thoughts, anyone?

The indicated voltage stayed between 13 ¾ and 14+. The needle was at least touching the 14 mark the whole way.

The transmission shifted without drama. There were no harsh shifts, and no being stuck in gear. I would have expected at least the harsh shifts to have shown up by now, if they were going to show at all.

I’m going for one more test drive tomorrow, just to be sure. If it’s similarly uneventful, I’ll feel like the Burb’s ready to make the trip on Monday.

Sounds great, good luck!

 

[Erik the Awful]

And that it *is* possible to quantify very small amounts of circuit
resistance in milliohms reliably. (or large amounts of conductance in mhos,
take your pick.)

Alternatively you can measure voltage drop, and you can do it without a milliohmmeter. I'm glad you took my ribbing in the spirit it was sent in.

For everyone else spectating, us AGE troops referred to Avionics as "pointy heads" because they were taught all sorts of engineering-level stuff. If they really wanted to be d!cks they'd point out that their career field required a higher ASVAB score to get into. They viewed us AGE guys as hammer-wielding-repair-monkey-artists. They could never figure out how we fixed electrical circuits with hammers, but they also didn't want to get close enough for us to fling poo at them, because we definitely would. AGE is actually pretty close to Avionics in ASVAB requirements, we just never got the same respect because we didn't turn wrenches on the aircraft themselves.