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323: How To Turn $6 into $10,000 (I Know, That's Click-Bait)
323: How To Turn $6 into $10,000 (I Know, That's Click-Bait)
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About this episode
Discover how a simple $6 incandescent test light can be a powerful diagnostic tool in automotive electrical work. Sean Tipping shares practical tips on using the test light to load circuits, activate relays safely, detect shorts, test sensor signals, and even check for spark when working solo. He emphasizes understanding the tool's current draw and limitations while demonstrating its versatility beyond basic voltage checks. This episode blends hands-on advice with real-world examples, showing how mastering this inexpensive tool can significantly boost diagnostic efficiency and earnings.
Topics:
incandescent test light
electrical diagnostics
loading circuits
relay activation
short circuit detection
sensor signal testing
spark testing
current draw understanding
diagnostic tool tips
automotive electrical troubleshooting
Cars:
Pontiac G6 Convertible
For real though, I'll share my favorite 6 dollar diagnostic tool that can make you a ton of money if you understand electrical fundamentals. I'll cover why I like it so much in day-to-day diagnostics and some lesser known uses as well. Listen to find out what it is...
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Pontiac G6
"...ound that out was by accident. I was diagnosing a Pontiac G6 with a accelerator pedal issue."
Select text to request an explanation
Welcome to the Automotive Diagnostic Podcast.
We're going to explore ways to sharpen our diagnostic skills, find learning resources, and hear from
experts in the automotive field.
This episode is brought to you by L1 Automotive Training and Keith Perkins.
If you're looking for education on module programming, J2534, eProm work, key and immobilizer,
electrical diagnostics, or drivability diagnostics, Keith has a website, L1Training.com, that's
got over 60 hours of training videos on all those subjects and more.
When I first started out doing mobile, I utilized Keith's videos on module programming and J2534
in order to get my head wrapped around what I would need for the tooling, the computers,
the software setups, what kind of obstacles I would be up against when I'm out there
programming modules on cars, and it was a huge benefit to me.
I continue to use the training videos that he has on his website.
I strongly recommend checking out L1Training.com.
The link is in the show notes.
Hey, what's going on, Automotive World, welcome to another episode of the Automotive Diagnostic
Podcast.
My name is Sean Tipping.
I'll be your host once again for this week's show.
Thank you so much for joining me.
You got just me on the show this week.
I'm going to be talking about one of my favorite tools that only cost you $5.95
if you go on Amazon, buy the same one I did.
And yes, I realize the title of this episode is a little clickbaity, but it's true.
So I will say that if you buy this tool and you learn some basic electricity fundamentals
and then you go out there and you find diagnostic work, this tool will make you
that much back and you got to have enough work to do.
So how did I calculate this number?
Well, first off, okay, what's the tool?
It's a test light, an incandescent test light.
All right.
I'm going to turn the episode off right here because you're like, okay.
But I'm channeling my inner Paul Danner for this episode.
But like really in real life, I use this freaking tool all the time and I try to convince
everyone else who's doing 12 volt electrical diagnostics on anything, even up to a 2025.
I don't care to use one of these, have it, use it.
It's an awesome tool.
If you understand electricity, you understand what it does.
It's huge.
And that's what I'm going to talk about today.
How did I get the $10,000 number?
Did I just pull it out of thin air?
Not really.
I looked at the total amount of diagnostic dollars I have done up until like right now
in 2025.
And then I did some rough math to figure about how many of those I utilized the test light
in the diagnostic.
Now probably only a handful of those I did just with the test light, right?
Generally you're going to have a scan tool involved in just about every car.
And if you include the pre scan, okay, I have it involved in every diagnostic.
But some of them did I need the scan tool to get there?
Probably not.
But how many diagnostics did I use the test light in determining what was going on
with the vehicle?
Maybe it was the only thing that I needed.
I bet you that number is conservative, to be totally honest.
I was generous on the conservative side of things when I came up with that number.
Plus it's a nice easy round number.
$10,000 sounds great.
Okay, but seriously, you can turn a $6 tool into $10,000 with your knowledge
and enough broken cars in front of you and people that are willing to pay you
to repair them or at least diagnose what's wrong with them.
So let's get into it.
How do you use this tool in diagnostics?
And maybe you already do and you're like, I don't really care.
I understand how to use a test light.
But I'll share with you today.
Maybe a few ways that you haven't considered using an incandescent test light.
Or maybe you just love to use some other tools out there.
Scope, PowerProbe, the LED test light, I don't know.
There's a bunch of other tools out there.
But I'm here to try to convince you why an incandescent test light is really
useful beyond just the normal things that you would think of.
Now, one of the biggest reasons I love to use a test light in most applications
is because it commands a load on the circuit.
And if you've taken one of my classes before I have an electrical analysis or
circuit analysis class where I talk about a bunch of different ways to assess
electrical circuits and how to think about electrical circuits.
And I break it down into two main categories.
Either that circuit is sending information or the circuit is performing work, right?
So if you think information like a data circuit for canned communication.
If it's doing work, think of a headlight bulb, right?
We're talking heat, motion, magnetism, something like that.
We're performing some sort of physical work.
And I think about those circuits differently and I treat them differently.
And I may test them differently.
And for any circuit that does work, I want to be able to load that circuit to make
sure that it can carry the current in order to do the work, right?
Whatever the load or loads in that circuit are, I want to make sure that that
circuit has the ability to carry the current to said load, right?
And a test light is a great way to do that, not the only way.
And of course, you have to consider what is the actual amount of current
that said load uses and does my test light equate to that, right?
You could have a situation where your test light draws more current than the load
in the circuit, but you could also easily have the situation where your test light
does not draw anywhere near the amount of current that a particular load uses
in a circuit.
So then, well, okay, well, how useful is it at that point?
You'll have to consider that.
Of course, that all starts with, well, understanding a couple of things here.
And I want to start with this.
And I've had this in my class.
I probably talked about it on the show before.
I did this when I was teaching at the college.
It's a really powerful example of why the test light's important in a lot
of circuit testing.
And like, I remember when I first experienced this out in the field
because I didn't realize this at first when I was out there testing stuff
with my meter, and this could be with a scope, too.
But try this.
Take your meter, take your scope, whatever, whichever one of those two
you're measuring voltage on a circuit, right?
Okay, 12-volt circuit.
Take a jump pack or a battery.
Doesn't matter.
Hook your black lead of your scope or your meter up to the negative
terminal of the jump pack or the battery.
And then take the red lead and hold it in your left hand,
and then touch the positive terminal with your right hand.
You will measure pretty close to battery voltage on that meter or scope.
Okay, it's going to depend on the impedance.
The scope's generally going to be a little bit lower than the meter.
But a meter will show you 12-point something volts on a fully charged battery.
Okay, that's through your body.
Switch the meter over to ohms, measure the resistance.
You're going to be like a million ohms of resistance or more.
It depends on how hydrated you are that day.
And you know for sure you're not going to be able to carry any usable
current for a circuit that needs to do work through your body.
But open circuit voltage testing, that's why you really shouldn't do open
circuit voltage testing.
You want to use your voltage drop.
There's plenty of classes out there on that.
But hey, maybe you don't know the circuit is open in the car, right?
That's a real potential thing that you could run into.
The fact of the matter is, you can read voltage through a large amount
of resistance on a circuit that is open.
Okay, if it has that unwanted resistance through your body, you can read that.
A test light will not light.
Try the same thing with a test light.
It's not going to happen.
Your body will not carry enough current from a 12-volt system to light
that test light.
It's just not going to happen.
So your test light would show you that like, hey, this isn't a usable path
for current.
We can't perform the work where your meter or scope,
unless you understand what's going on.
You understand the limitations of your tool, which is key.
Any tool really just depends on you understanding the limitations
of what it can and can't do.
But the meter or the scope in that instance is not going to be able
to tell you what work the circuit can do.
Again, voltage drop testing aside, assuring that the circuit is complete
and then doing voltage drop testing.
You can definitely assess what you need to from the circuit that way.
But I like to test light.
Just personal preference is the way I use it.
So that's it.
Test light is going to be able to load the circuit,
demand some amount of current to basically stress test
that circuit to say, hey, do we flow current?
Now, how much?
That's really important, right?
What is the normal amount of current
that should be flowing through that circuit?
And what is the normal amount of current
that my test light would flow if I just hooked it up
to a battery?
You should know that.
Whatever test light you're using,
and again, incandescent bulb,
you should put an amp clamp around it
and figure out how much current it draws.
If you have multiple test lights, test them all.
Write it on there with a piece of tape
so you don't forget it, okay?
This one's 0.2 amps.
This one's 0.02 amps.
This one's an amp.
You can put some bigger bulbs in these things.
They will mount the plastic eventually if you leave them
on, so do keep that in mind.
Headlight bulb, right, four amps, right?
That's not quite a test light, but it is.
There's tools out there where you can set up the test light
in like a plastic holder, the 3D printed.
Kind of just becomes a real high-amperage test light,
but you're gonna wanna know that to say,
A, is it equal to the load that is normally in that circuit,
but also for safety reasons,
if we're testing computer-related circuits,
we also wanna know how much amperage that test light
is going to draw when connected to the circuit
because in the instance of a headlight bulb,
that's gonna be way more than that circuit is designed to handle
and then you let that smoke out of the inside of the computer
which you obviously don't wanna do in testing,
creating another expensive problem on top of the other one
that you're trying to solve.
So do be aware of what your test light draws,
but once you know,
and if you're able to assess the current
that is normally in the circuit,
this becomes a really powerful tool, okay?
So again, just checking to see, hey, can that circuit
carry a load enough to light up my test light?
Now the brightness of the light
is obviously gonna depend on the voltage,
not only on the circuit, but in the system
and the bulb itself.
So that's where there is a weakness in the tool
of are you gonna be able to tell a two-volt difference
from your test light?
I don't know.
You'd have to be pretty freaking good
to be able to tell that unless it's changing in real time,
I don't think I could pick that out, to be totally honest.
So that's where meter or scope is gonna be more useful
as far as like voltage drop testing.
And I'm not saying this is the only tool that you should use.
I'm just making a pitch for like why this should be
in your regular repertoire of tests and tooling
that you use on a vehicle.
This show is brought to you by Automotive Seminars.
If you're looking to stay up on the cutting edge,
diagnostic strategies and techniques, this is the place.
You've got live four-hour seminars that are put online
that you can join in, ask questions,
interact with the instructors.
With some of the best of the best,
they've got Keith Perkins and John Thornton
putting on classes like Network Diagnostics,
Mechanical Engine Testing, Advanced Electrical Testing
and GDI Diagnostics and a ton more.
And once you purchase one of these training seminars,
you can access this at any time that you want
through your account at automotiveseminars.com.
You can rewatch the training a year, two years later,
which makes this training even more valuable.
So I highly recommend you check this out.
The link is in the show notes.
All right, so most of you know this.
You've used it, you got one, either you like it or you don't,
but you're aware of this style of tests.
But for today's episode, I thought I would share
just a couple uses of a test light
that make it more versatile than you might think.
All right, now again, really important here
that you understand the amperage draw of your test light.
But for a test light that's somewhere
between 100 to 200 milliamps of draw,
this is one of my favorite tools
for activating a relay circuit.
Okay, what I mean by this is quite often
relay control circuits are gonna be controlled.
They'll have either constant power ground on one side
and then they're controlled by a module
either by providing power or ground to that relay coil.
You can use a test light and provide either ground
or power, whichever one it needs,
to that circuit to activate the relay coil, okay?
Now, here's why this is a safer method
than just jumping straight up power
and ground to that circuit, okay?
Well, if you're incorrect and you thought
it was supposed to be power, but you did ground,
that's gonna be real bad for the driver
in that control module.
But if you do it through a test light
that again is somewhere between 100 and 200 milliamps
which is the normal relay coil draw for most relays
there are exceptions.
So I guess I should just put a disclaimer out there.
There's still a possibility you could ruin a control circuit
on a computer this way.
So just be cautious.
You can research the relays if you really want to
and find out what the normal amperage draw is.
But I have found, again, if you're in that like
150, 160 milliamp draw, that's the normal current draw
for the control side of a relay.
So you're usually safe, okay?
But also pay attention to your diagram
and make sure you're applying the same thing.
And then that way, if the circuit normally applies ground
to the relay and you're providing ground, you're safe.
And I guess you don't need a test light in place.
But anyways, I'll use a test light just again
as a safety measure when I'm doing this,
when I'm jumping it to a circuit
that's connected to a computer
and I want to test it out, right?
I want to be the computer on turn on the relay.
I'll use a test light in place.
And it works really well.
There's still enough current
that will go through your test light
and through the relay coil to activate the relay.
Try it, it works really well.
Again, it's gotta be an incandescent.
An LED one is not gonna work for this.
Now, the way that I actually found that out was by accident.
I was diagnosing a Pontiac G6
with a accelerator pedal issue.
And it was a short circuit
to ground on the five-volt reference
for the accelerator pedal.
And what I was doing is I was using my test light
to see if I had a straight shot to ground.
And this is another use for your test light, right?
If I power up my test light
and I touch it to something
that I think maybe has a ground on it
and it lights up brightly,
I know that that is a direct path to ground.
And I will use that for checking
both power and ground on circuits, right?
Let's say I have 12 volts on something
and I'm not sure is this like battery voltage
or is this a bias voltage?
Ground your test light, touch it.
Does it light up your test light or does it not?
That's gonna be a real quick way to say,
oh, okay, this is a bias voltage
maybe provided by a control module
or oh yeah, this is straight power, okay?
I've done that on a canline before.
Both power and ground, right?
I'll power up my test light.
If I have a no-com and it's at zero,
I'll touch the canline.
And if it lights up, okay,
I got either a straight shot to ground
or a straight shot to power enough to light a test light,
it is shorted to something, right?
Either inside of a module or on a wire,
I am shorted directly to something.
That's the only way it's going to light my test light, right?
I understand what's necessary
in order for enough current to flow through that circuit
to light up my test light
that it's gotta be a direct short.
Or again, oh no, this 12 volts is a bias
or at least it's a resistive short.
It's got resistance in between it
and it's path to either power or ground.
But anyways, on this Pontiac,
when I powered up my test light,
so the clippy ends on the power
and so I'm touching the circuit
with the end of my test light to see
is this a straight shot to ground?
It activated a relay
and that relay was for the brake lights.
And so by determining that,
I was like, oh, it has to be this circuit, right?
I'm grounding this relay by touching this wire.
These two wires have to be touching.
Where do they go together in the harness?
And then I was able to find the short.
And it was a poor wiring repair
and a wire was sticking out
from the control side of a relay
to the five volt reference on the accelerator pedal.
And that was how I realized, I was like,
oh, a relay is a great way.
A test light is a great way to test a relay.
There's enough current to activate said relay.
I could hear it click every time I touched it.
So it works really well.
Another way that I will use a test light.
And this one you maybe could consider
a little bit more risky.
However, I've not had any issues doing this.
So you'll probably call me up tomorrow
and say, hey, I just ruined this network by doing this.
But when I'm at a control module
that maybe is not communicating, all right?
So driver's door module just did this other day.
I'm gonna use my test light.
I'm gonna check power.
I'm gonna check ground, okay?
That's what I need.
Now there's communication to this module as well, okay?
Now it could be can, could be Linn, whatever it is.
I'll take my test light, grounded.
I will touch it to the network wire.
And I'll do one of two things.
I'll either just listen with the key on
for things to ding and the dash to go crazy
as soon as I do that.
Because what am I doing?
I have a grounded test light touching it to the network.
I'm pulling that network down, but I'm doing it safely.
Now with a can network, you'd probably be okay
just straight up grounding it.
But this is giving you just another layer of safety
because the test light again is not going to be able
to flow much current through that circuit.
But it'll pull it down.
It'll stop communication.
What does that mean to me?
If that happens, that means up to that module
where I am testing, the circuit's good
on the communication wire, right?
If it's a single wire GM LAN, I do that.
I hear everything go crazy.
Well, my network's connected here, right?
Should I scope it?
Is there a possibility for some weird corruption?
Sure, that's possible.
But what it tells me at least is the circuit's connected,
okay?
So again, power ground and touch it to the network.
You're good to go.
You at least know if the circuit is connected
up to that point.
With can, if you wanna be even safer,
you can just jump the two wires
at the module you're testing.
Jump them together and do the same thing.
There definitely won't be any significant current flow
through that circuit.
You're just jumping can high and can low, perfectly safe.
I've never seen that cause a permanent issue.
But as long as they're jumped,
whatever else is on that network
ain't gonna communicate.
And depending on the network that you're working on,
there's probably other modules
where if you have the key on,
they'll respond by doing something.
I mean, use your scan tool, right?
Have your scan tool right there,
jump them together at the module you're testing
and see, okay, I just lost everything else
on that network.
Okay, circuit's connected all the way up to this point.
I mean, it's a down and dirty test method.
Is it gonna maybe miss some things at some point?
Sure.
Does it work for a quick check?
Sure does.
You can also use a test light.
I'm gonna keep going here.
To change the voltage on sensor signal wires.
Okay, what do I mean by this?
If you have a five volt sensor,
or I mean, it could even be higher than a five volt sensor,
but you have a five volt sensor
and it's meant to output a voltage to the PCM.
Normally you'll have one of two things
on that signal wire going to the sensor.
You may have zero when the sensor's disconnected
and that's normal.
You could also have five volts on that signal wire.
You'll have a separate five volt wire
as a reference to the sensor,
but then some sensors will have five volt present
even on the signal wire that is a bias from the computer.
In the case of a Hall Effect sensor,
maybe it's meant to pull it down.
I've seen other sensors that just have that five volt
bias.
I'm guessing it's more for like a circuit integrity check.
But anyways, you can take a grounded test light
and pull that down, right?
If it's a crank sensor and you've got a five volt bias
and the sensor normally pulls it down,
touch it real fast on and off and watch your scan tool
and you can then be like, oh, okay, this circuit is good.
I see the RPM when I'm, as the faster I go,
the faster the RPM goes on the scan tool.
Cool.
And again, safe thing to do on that circuit.
I've never damaged a circuit by doing that.
It's essentially the same thing the sensor's doing
in that point.
The sensors probably actually just pulling it all the way
down to ground where you have a resistive path
within your test light.
But you can do it the other way too,
you can power up your test light, clip the end on power,
and then touch it and you know,
the voltage should jump up, right?
So for a signal wire, like a map sensor,
now you could also just jump the five volt reference
to it and that probably would do the same thing,
but test light will work as well.
And I've done that a lot of circuits
to verify the integrity.
I'll watch the scan tool, look at the voltage,
touch it with the test light,
that's either power up or grounded, watch for a change.
Okay, I know that that circuit has enough integrity
to read what's happening on this end
and I move on from there.
Another thing you can do with the test light,
this might be my last one here.
I'm sure many of you have done this
where you take the test light, you ground it,
and I think you can actually clip it to positive too,
but I usually will ground it
and then I can do a spark check with it.
Now, make sure you're hanging onto the plastic part,
not the metal part, but if you're cranking an engine over
or the engine's running and you move the metal end
of the test light close to the output
of the ignition coil, the spark will jump
from the ignition coil to the end of your test light
in a visible manner so that,
and you can even change the range, right?
You can have an adjustable spark tester with that test light
and you can see it and you can hear it
and you can feel it if you want to.
Stick your other finger in there and see how it feels.
Ah, that's 30,000 volts.
All right, that coil is good.
But what I like doing here,
this is one of my favorites for when I am by myself,
right, I'm doing mole work, I'm on the parking lot,
I don't have anybody else around to crank the vehicle,
I will take my either a long wire
or I have a reel of wire and I'll take
the end of that lead and I'll stick it
into the ignition coil, right?
I want to see if this engine has spark
because it's a no start.
I will stick it into the end of that ignition coil,
I'll bring the other end of that lead,
clip it to my test light
and then I will find the bolt in the door jam, right?
The driver's door and I'll make sure
that it's not painted, you know,
scratch off a little bit of paint if you need metal
but you want a good metal surface
and I'll hold my test light
about an eighth of an inch away, quarter inch away,
whatever, again, we can adjust the range
for our spark test here and I'll crank it over.
So I'm in the driver's seat so I can reach the key,
I can hit the brake pedal, I can hold the test light
and I look for spark and it'll jump right to that bolt
in that door jam if there is spark
through the wire, through my test light to that bolt.
It is a great test to test for spark
if you're by yourself and you don't want
to pull out your scope just yet,
you're just doing a quick check to see,
hey, do I have spark?
It works really well, right?
Now, again, you can do this under the hood
if you have a helper to crank,
but if you're by yourself,
real quick method to check for spark.
So it's a real quick episode today.
Those are my uses for a test light.
Let me know what you have.
If there's something I forgot about, didn't mention here.
I would love to hear your ideas
or your ways that you use a test light
in your day to day diagnostics
and how if you've made $10,000 or more
from this little six dollar tool
and again, $5.95 is the price on Amazon,
I'll send you the link if you can't find it.
With that all the way,
let's get out there and start fixing the world
one car at a time.
Let's go.
Let's go.
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