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Old 12-28-2017, 02:44 PM   #26
JohnLane
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Originally Posted by swedefiend View Post
I totally disagree.

I was taught the exact opposite. Test lights are just for quick checks. When it comes to actual diagnostics - DVOMs are king.

Too many times, someone says "I tested it (with a test light)" and the problem is that test lights will light up at 11 volts and higher with very little degree of indication of how low the voltage actually is.

Now, Snap-On makes a test light with a a voltage gauge on it. That is nice
I like the test light as it pulls enough current in many cases to know that there may be a bad connection that the DVOM says "12.5 volts here... Keep looking."

Obviously there is a place for the DVOM.... More often then not in the toolbox taking up space.

OP... Glad you managed to solve that common problem.
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Old 01-02-2018, 03:05 AM   #27
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One of my cars failed similarly, and it was the fuel FILTER.
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Old 01-02-2018, 06:07 AM   #28
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The in tank fuel pump fails when its warmed up. Solved
So, to get home when the car's warm, you have to spray starting fluid into a vacuum line? Also, dude, get a can of PB, some new exhaust studs and nuts, as well as exhaust port gaskets. Fix that exhaust leak. That way, people on FB don't keep going when they see your video on the carthrottle page.
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Old 01-02-2018, 01:24 PM   #29
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So, to get home when the car's warm, you have to spray starting fluid into a vacuum line? Also, dude, get a can of PB, some new exhaust studs and nuts, as well as exhaust port gaskets. Fix that exhaust leak. That way, people on FB don't keep going when they see your video on the carthrottle page.
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Old 01-02-2018, 01:42 PM   #30
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The in tank fuel pump fails when its warmed up. Solved
Read your opening post and then try to come up with how the in tank pump could cause the issues you are having. I think you want to believe that you have found your problem.
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Old 01-02-2018, 02:18 PM   #31
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Originally Posted by swedefiend View Post
I totally disagree.

I was taught the exact opposite. Test lights are just for quick checks. When it comes to actual diagnostics - DVOMs are king.

Too many times, someone says "I tested it (with a test light)" and the problem is that test lights will light up at 11 volts and higher with very little degree of indication of how low the voltage actually is.

Now, Snap-On makes a test light with a a voltage gauge on it. That is nice
There is a place for both the test light and the dvom. Test light is actually better in most cases because it also verifies current . I had a window regulator recently that was non operational and I made the mistake of using a dvom to measure voltage, got 12v, installed a new window regulator/motor and it didn't work!@$%. There was a bad connection in the door umbilical, and even though I read 12 whole volts, it wasn't passing enough current to light up a test lamp, or a noid light. Learned my lesson on that one!

There are even test lights now that don't even have a ground wire. Your skin touching to a good ground completes the circuit from the lamp to ground.
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Old 01-04-2018, 10:51 AM   #32
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Default The test light

I have been formally trained to use the test light to verify circuit operation.


A good use of a dvom is to check for more than 5 ohms resistance in a ground circuit. Or another example is connect to each end of a wire and wiggle test the harness to check for broken wires which may show up as fluctuating resistance.

Last edited by ZVOLV; 01-04-2018 at 11:04 AM..
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Old 01-04-2018, 09:44 PM   #33
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The bottom line is this:

A test light will show you quickly that there is voltage present in a circuit.

A DVOM will quantify voltage, current, Hz and more in the same circuit.
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Old 01-04-2018, 09:46 PM   #34
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Also know that there are times that using a test light can induce operation in a circuit by providing an auxiliary path to ground.

A high Z meter will NOT do that.

Last edited by swedefiend; 01-05-2018 at 02:21 AM..
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Old 01-04-2018, 10:32 PM   #35
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So let's say you want to verify if a washer pump circuit is good....take out the meter? Ok so you measure 12v at the pump wiring between positive and the negative. Is the circuit OK?
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Old 01-04-2018, 11:46 PM   #36
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So let's say you want to verify if a washer pump circuit is good....take out the meter? Ok so you measure 12v at the pump wiring between positive and the negative. Is the circuit OK?
Id use a light if I can get the connector loose. But, I'd use my meter with piercing leads if not.
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Old 01-04-2018, 11:51 PM   #37
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Also, nine times out of ten, the pump is bad or it's the ground.

Measure resistance across the pump. High resistance? Seized armature. Infinite resistance? Brushes shot.

If in spec (have to measure a good one or look it up), measure voltage at connection using power and ground from connection. Then, measure voltage using ground at battery. Significant drop? Clean ground, move to fuse block.
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Old 01-05-2018, 12:13 AM   #38
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Just going to leave this here...

Electrical Automotive Troubleshooting - Diagnosing Voltage Drop @ fluke.com

edit:// Because this is a complex topic best *not* left to me to touch on - especially right now (work).

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Old 01-05-2018, 10:41 AM   #39
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Originally Posted by swedefiend View Post
Id use a light if I can get the connector loose. But, I'd use my meter with piercing leads if not.
Ok so you have now pierced the washer pump wiring and registered 12v between the positive and negative wire, while pressing the switch. Pump is not operating. Replace the pump?

How do you know there isn't a bad connection at the fuse block or a poor ground? Recently I have been becoming a bigger fan of the noid light. Just clip it in and walk back to the switch and then see if it lights up. No bulky wires, or meters, or lamps dangling.

There are times for using each tool. Using a test lamp on computer circuits isn't a good idea, but on higher power stuff like motors I'm using a test light to confirm voltage and current.

Last edited by ZVOLV; 01-05-2018 at 01:10 PM..
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Old 01-06-2018, 09:04 AM   #40
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Qualifying vs Quantifying.

Indeed. Different tools for different jobs.
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Old 01-06-2018, 09:05 AM   #41
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PS, I would never replace that pump without bench testing it first
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Old 01-06-2018, 01:44 PM   #42
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Quote:
Originally Posted by swedefiend View Post
Qualifying vs Quantifying.

Indeed. Different tools for different jobs.
I am starting to use my LED test light more and more. Recently, I confirmed an ECU controlled circuit with a bidirectional scan tool and my LED test light and confirmed the power wire was good and the PWM low reference side was good. Condemning solenoid!
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Old 01-06-2018, 04:34 PM   #43
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I am starting to use my LED test light more and more. Recently, I confirmed an ECU controlled circuit with a bidirectional scan tool and my LED test light and confirmed the power wire was good and the PWM low reference side was good. Condemning solenoid!
I have a really nice meter with sweep, record, min/max, etc. (So this obviously biases my approach to diagnosis).

It was a (incredibly useful) gift from my dad when I started working on cars. The scope I bought for myself was not as useful...

Anyway, there are more ways than one to peel a banana :-)
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Old 01-07-2018, 11:52 AM   #44
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I just got a large jaw amp clamp to connect to oscilloscopes to do relative compression testing. Next time I suspect a dead hole deep in an engine and I don't wanna pull the plugs...busting out the scope!

I still maintain that a cheap test lamp is a better tool for measuring B+ power to a component such as a tank fuel pump. OP could measure 12v on a Fluke meter and the pump still may not operate.
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