FEGEITOK:
Forgive my backyard statistics

But it seems to me that 99.9% of local car electronics/electrical technicians use only a test light to try to troubleshoot issues

When service manuals usually recommend multi-meters for tests?

Which would you rather have?

Can a test light substitute for a multi-meter?

I think for me the answer is multi-meter. But just how do they get to sort out issues with just a test light and without consulting factory manuals?

I want to learn oooo

tutuwater:
What is with abusing people using a straight forward light bulb tester. It is more effective to use a light bulb tester in checking for shorts and leakages. A multimeter has its own purpose too. Use what you are familiar with and stop abusing others.

GAZZUZZ:
both have a role to play in diagnosis.

GAZZUZZ:
both have a role to play in diagnosis.

Siena:


Does a light bulb tell you what voltage you're reading? Does it tell what the polarity is? We're talking bulb here, not an LED.

Just so you know, a bulb has a hell of a lot more internal resistance than a digital multimeter. Measure across the 5V reference outputs from an ECU, and you could kill it. Same goes for measuring V in sensitive modules like instrument clusters, ABS modules, TCU's etc.

I have not had a test bulb amongst my test equipment for over 2 decades. I do have an LED power probe, and I seldom use even that. Voltmeters, oscilloscopes or picoscopes are all safe to use, and I rely more on these as modern systems become more complex, and measured voltages become smaller. Try measuring 900mV with a 12V 10/21W tungsten bulb, and see what the results are.

A technician who will not invest in a digital multimeter that starts from as low as £4.99 is a cowboy.

Siena:


Does a light bulb tell you what voltage you're reading? Does it tell what the polarity is? We're talking bulb here, not an LED.

Just so you know, a bulb has a hell of a lot more internal resistance than a digital multimeter. Measure across the 5V reference outputs from an ECU, and you could kill it. Same goes for measuring V in sensitive modules like instrument clusters, ABS modules, TCU's etc.

I have not had a test bulb amongst my test equipment for over 2 decades. I do have an LED power probe, and I seldom use even that. Voltmeters, oscilloscopes or picoscopes are all safe to use, and I rely more on these as modern systems become more complex, and measured voltages become smaller. Try measuring 900mV with a 12V 10/21W tungsten bulb, and see what the results are.

A technician who will not invest in a digital multimeter that starts from as low as £4.99 is a cowboy.

Siena:


Does a light bulb tell you what voltage you're reading? Does it tell what the polarity is? We're talking bulb here, not an LED.

Just so you know, a bulb has a hell of a lot more internal resistance than a digital multimeter. Measure across the 5V reference outputs from an ECU, and you could kill it. Same goes for measuring V in sensitive modules like instrument clusters, ABS modules, TCU's etc.

I have not had a test bulb amongst my test equipment for over 2 decades. I do have an LED power probe, and I seldom use even that. Voltmeters, oscilloscopes or picoscopes are all safe to use, and I rely more on these as modern systems become more complex, and measured voltages become smaller. Try measuring 900mV with a 12V 10/21W tungsten bulb, and see what the results are.

A technician who will not invest in a digital multimeter that starts from as low as £4.99 is a cowboy.

erico2k2:

Bro nor fall my hand ohh

cocoduck:
test light (scope on a rope, lol), DMM and oscilloscope and scan tool are the four basic diagnostic tools a technician needs for the trade.

GAZZUZZ:


Both have a role. Knowing when to use which is important. Quick diagnosis of "certain" circuits can be done with ease using a 12v bulb, with the right rating. Nothing about falling hand, just being realistic. A DMM will give you voltage, a bulb will give you a perception of the amount of current you are working with.

FEGEITOK:


Voltmeters, oscilloscopes or picoscopes - how much do these cost for DIYs not professional level?

isn't the voltmeter embedded in the DMM? Do I need a dedicated voltmeter?

FEGEITOK:
After I called a local electrical tech to help me fix a short which I earlier posted about.

I stayed back to observe him and every time he performed an action my heart would sink.

He kept throwing away factory rubber shields, cutting wires here and there, and probing pins

The next day my MAF failed, I do not know if it is a coincidence or it is his use of 12V via the test bulb to keep probing the various components

The one that made me not ask him to come back was when he wanted to start working on the ECU while the battery terminals were still connected.

Thankfully, he came in the afternoon and when he said he would have to come back the next day to complete, we haggled over pricing

Then I paid him 50% and he left, I gathered all the insulators he threw away and tried to return everything as closely as possible to how it was when it left the factory and didn't allow him to touch the ride again.

I think that his work destroyed my MAF, I cannot say for certain.

But I cannot allow him to cost me an ECU in the name of fixing shorts

erico2k2:

wen u say test l ight hope you dont mean light bulb

FEGEITOK:


Voltmeters, oscilloscopes or picoscopes - how much do these cost for DIYs not professional level?

isn't the voltmeter embedded in the DMM? Do I need a dedicated voltmeter?

erico2k2:

how can a light bulb give you an accurate reading of current? GAZZUZZ as U know Im not a Mechanic but I am Engineer so I work with this day in day out so I can vest my experience in this part U nor go win dis one bross.How can light bulb tel U the direction of flow?
How can a light bulb test any component wen the procedure requires one terminal of the battery being removed?

GAZZUZZ:

Both have a role. Knowing when to use which is important. Quick diagnosis of "certain" circuits can be done with ease using a 12v bulb, with the right rating. Nothing about falling hand, just being realistic. A DMM will give you voltage, a bulb will give you a perception of the amount of current you are working with .

cocoduck:
hahahahaa of course I mean a light bulb, because there has to be a current flow, but it must be done with a wiring diagram.
Remember Current V=IR
V is voltage or pressure or potential difference

I is Current or the main little devils themselves

R is resistance or the opposition to the flow of the little devils.

So sometimes you will need to load the circuit to test its integrity. You must do it with a wiring diagram so as not to cause more trouble.

GAZZUZZ:






perception meaning:


Using a lamp to test for voltage in failing circuit (not ECU related) is quicker and more accurate than using a DMM, the meter might always give you a 12v reading if you were searching for voltage, but a lamp might not glow as bright as a 12v feed straight from the battery. That's where perception comes in. I have a DMM, actually several, but a lamp with the right rating is a winner any day.

erico2k2:

Ok fair enough but like what circuite in the car?

GAZZUZZ:


anything that is not powered by an ecu and utilizes 12v. I have a lot of lamps for different diagnosis.

erico2k2:

Ok fair enough I can see how that works, but what would you say with someone testing and ECU powered components as simple as a fan switch relay with a bulb?would that not amount to an attempt to fry the ECU

erico2k2:

, Ok I understand what you mean and in a way I'm so sorry for using the word QUACK,I have had a moment of rethink.
On a diff note that's try error procedure.This what the rewire does, they end up frying your ECU,well if you get teh heart you can continue but if you come across a well informed customer and you fry their components you don enter one chance be that
But you do know there is a probe for this right and it doesn't cost a arm and leg,these are cheap,I wil love you to buy these if U are into it.
ie this bellow

Siena:
Lots of modern cooling fans are shifting away from the traditional fuse and relay set up, where they were pretty much stand alone systems, with a radiator-mounted thermo switch.

My 2000 Audi A4 4.2 V8 Quattro actually has a stand alone cooling fan control module. The circuit is also linked to the climate control panel, and testing voltages other than the fat 12V direct to the fans with a bulb, will pop not just the control module, but also the digital climate control panel. I have come across folk who have popped these testing the circuitry with an analogue voltmeter, which has no internal power, and relies on voltage from the component you're checking for voltage at. These have less internal resistance than a bulb, yet they are still capable of wrecking any semi-conductors.

Then there are cooling fans which are actually controlled by the engine ECU, via the CTS. You don't want to be testing this with a bulb. Yes, there are parts of a circuit that have a direct 12V+ feed. But, for the avoidance of errors, test bulbs are frowned upon in the industry. A competent technician should learn to interpret readings with a digital multimeter, LED power probe, oscilloscope or picoscope.

Dealerships here supply SST's, so every tool required for testing is available to all their technicians. If an audit was carried out, and a tech was found testing circuitry with a bulb, he / she would get a disciplinary, and the dealership would be marked down on the audit. I have seen that happen countless times.

I had a technician from a local garage testing pulses to injectors using a bulb, and of course, he got nothing. He ripped out the wiring harness, and when replacement gave the same results, he concluded the ECU was bad. £1200 later, the car still wouldn't run. This is when the car was towed to my place. The fault? A blown 15A fuse that feeds the switched 12V+ which is common to all the injectors. This was in a 2009 Mercedes-Benz E320. Cost of repair? Half an hours labour, and .76p for a fuse.

It could have been worse, God knows what this garage billed their customer (I didn't get to meet him / her).

cocoduck:
Op when I say test light, I don't mean the one you made on your own, because chances are that the bulb you will use will draw too much current, so you have to buy a professional test light with not more than 200mA ratings. According to Mr Paul danner (pbuh), computer electronics use 100mA, testing the circuit with a 200mA test light will not damage it, I doubted it and tried it and it worked, now, here is a practical way you can test it without a car, I remember a while ago I took an LED and connected it directly to a 12v battery, it just flashed for a millisecond or so and went out, so it got burnt, without any sign, then I took a resistor and connected it in series to another LED, this time the LED lighted up and stayed on until I disconnected it from the battery,I tried it on a tail light bulb, the bulb didn't glow,even a little bit, so I took the same resistor connected it in series with the positive lead of the DMM and connected it in series also to the battery and I still got 12v, even the other lead gave the same result, how do you explain this? It is simple, current has to flow, and current is not another word for volts. Paul danner has made several videos on how to test three wire Wheel speed sensor circuitry using a common test light (200mA maximum!) or use a resistor in series. You need to see those videos, they are free of charge.

Siena:
Lots of modern cooling fans are shifting away from the traditional fuse and relay set up, where they were pretty much stand alone systems, with a radiator-mounted thermo switch.

My 2000 Audi A4 4.2 V8 Quattro actually has a stand alone cooling fan control module. The circuit is also linked to the climate control panel, and testing voltages other than the fat 12V direct to the fans with a bulb, will pop not just the control module, but also the digital climate control panel. I have come across folk who have popped these testing the circuitry with an analogue voltmeter, which has no internal power, and relies on voltage from the component you're checking for voltage at. These have less internal resistance than a bulb, yet they are still capable of wrecking any semi-conductors.

Then there are cooling fans which are actually controlled by the engine ECU, via the CTS. You don't want to be testing this with a bulb. Yes, there are parts of a circuit that have a direct 12V+ feed. But, for the avoidance of errors, test bulbs are frowned upon in the industry. A competent technician should learn to interpret readings with a digital multimeter, LED power probe, oscilloscope or picoscope.

Dealerships here supply SST's, so every tool required for testing is available to all their technicians. If an audit was carried out, and a tech was found testing circuitry with a bulb, he / she would get a disciplinary, and the dealership would be marked down on the audit. I have seen that happen countless times.

I had a technician from a local garage testing pulses to injectors using a bulb, and of course, he got nothing. He ripped out the wiring harness, and when replacement gave the same results, he concluded the ECU was bad. £1200 later, the car still wouldn't run. This is when the car was towed to my place. The fault? A blown 15A fuse that feeds the switched 12V+ which is common to all the injectors. This was in a 2009 Mercedes-Benz E320. Cost of repair? Half an hours labour, and .76p for a fuse.

It could have been worse, God knows what this garage billed their customer (I didn't get to meet him / her).

erico2k2:

True
@ GAZZUZZ, I think this is what I found at with my fan hence I made reference to it.I think my car has one of those fans controlled by the ECU and not a fuse and relay set up.cos U can never directly run wires from the battery to it to make it work it wont work , I tried it, I ended up buying a brand new fan still did not work.Problem was a stuck heating valve and leaky radiator. 318Ci 2002

GAZZUZZ:


You connected direct voltage from a battery to a circuit without knowing the pinout. Not very smart.