Nope.....component inoperative....fuse checked good with test light....it was corroded and open and discovered when removed. I bent the tab out to show contrast for photo.... I know guys that have searched for hours until they pulled the fuse....That’s always the first thing I do after hitting it with my headlamp bulb converted into a test light. Headlamp bulb will load test circuit at the same time.....
And a good reason to throw your test light away. In my opinion they have no place in electrical diagnostics. Use a meter. Sent from my iPhone using H.A.M.B.
Even more important: Always put dielectric grease on the fuse before you put it in. Pull all of them and use dielectric grease
A test light does not give you a voltage reading, hard to tell if there is resistance somewhere trying to judge how bright the light is. The op said the problem was corrosion so a meter would have shown a voltage drop across that corroded area. Sent from my iPhone using H.A.M.B.
You still would have read 12 volts across the filliment in the fuse....the open was in the leg that was not discovered until the fuse was pulled....you could STILL read 12volts with one strand of wire still connected anyway....that’s why I also use a headlamp bulb instead of a regular test light....the headlamp will load test the circuit and find high resistance in a cicuit BEFORE a meter ever will if you’re only reading voltage. Unless you want to ohm out the entire circuit. The headlamp load test is a quicker alternative to find high resistance in a circuit......the bulb will only light dimly....it gives you a more “dynamic” view of what the circuit is doing.... A volt meter can’t do that, unless you test for amperage draw and not volts. You can also run this test with meter set to amps and headlamp test light substituting for your component/load. But why go through all that when a visual of a dimly lit headlamp/test light setup will give you your answer.....anyway.....a meter set to volts would not have found this problem without also doing a visual of the fuse......
I’ll make another video later showing the meter reading the same voltage with just one strand in the wire connected.....and if I have time today, I’ll make another headlamp test light and show how the meter will read voltage but the lamp will be dim....and also show an amp draw test on the circuit....with one strand....then whole wire.....it’ll give you all an idea of how I dynamically test a circuit.....some may use this method already..... I just hope to pass on some knowledge to some of the guys that find electrical work frightening.....
I have used the head light instead of a fuse for finding shorts Works great. Just because you have voltage does not mean you can pass amperage down the same path. I have seen industrial fuses blow but still show continuity with a dvom Also seen wires with large bubbles of corrosion or that have rubbed apart that pass a test light or voltage test but might only have 1 or two strands of copper holding it together. Big difference between having voltage present And that same circuit having the ability to let current flow.
Yep! That’s why I’ll always pull the fuse and look at it before moving on with diagnostics......I haven’t used my small test light in 25 years ( if I still have it ). Load testing with the headlamp bulb is a quick and easy way to dynamically test a circuit without using your meter set to amps.....I wired it up with a clamp on one end and nade a long pointed probe out of a coat hanger on the other.....it’s never let me down.....don’t misunderstand me.....sometimes a test absolutely calls for a metered amp draw check....
During my 33 year career of working on fire trucks the number one problem was a short/open in a part of the electrical system. The trucks I first maintained had horrible electrical systems. Kept me busy, but my number one tool was the test light. I had an arsenal of other test equipment, MAC short finder, 20 foot test leads, some with circuit breakers in them, etc. But I used my test light the most. My helper told me “ your not right.. you smile when one of those junkers come in with an electrical problem!” ....... to me it was like a scavenger hunt.... kinda fun. Might take me a while.. but I always found the problem! Just my experiences. Bones
I simulated a “high resistance” circuit and used a headlamp to demonstrate what the lamp looks like when testing. I’ve found it yo be a quick and easy test, even for those guys that don’t have a meter. I really hopythis info helps someone with their trouble shooting skills......
Same here! The guys thought I was crazy because I loved troubleshooting electrical the most! I guess we’re just odd.....
Electrical can be fun if you understand it. Most folks don’t “ get it” as you can’t see the electricity ( unless you let the smoke out) If you think of an electrical circuit in the same way as hydraulics or a water system and visualize the flow of current it makes it easier. I’m a little fucked up by our friend mr. Lukas working at jaguar for years you either got electrical or curled up in a ball in the corner of the shop and let out a big old dirty man cry on a daily basis !
An open will absolutely read the same voltage up until the open, if there is a resistance a volt meter will show a voltage drop across the resistance. Your light goes dim when there is a resistance because of low voltage. If you can tell what the voltage is by the brightness of the light you are better than me. There is nothing a light will do that can’t be done with a voltmeter, each to their own. I’m done with this thread now... Sent from my iPhone using H.A.M.B.
Van, Lucas , systems have “ghosts” built into them! My first experience was with my Triumph motorcycle back in the sixties. Tried to shy away from them ever since. Was horrified when I frist got into the electrical system in my 94 Dodge one ton and found “ Lucas “ printed on the turn signal. My current daily driver has that system and you never know what’s going to work or not work from day to day. Lol Bones
I guess I did miss something, If there was an open a light could find that for sure if you know what to look at, I'm not sure what you meant by using the light to load the circuit to find an open. to locate a short, absolutly, it loads the circuit to allow diagnosis. if the problem was high resistance, yes a bulb will show that because of the voltage used by the resistance. I stand by the fact that, in my opinion a test light has no place in diagnosis, again my opinion. there is nothing that can be done with a test light that a meter cannot do. whatever works for everyone else is great. The one strand of wire is great until you put a load on it, there will be a significant voltage drop across it. depending on the load of course. Maybe I did a poor job at explaining what I was getting at. Hell maybe I still am.
I totally understood your statement and agree a meter is “better”. But for me the test light was quicker and when you drop a test light from 10 feet, your out $10, my Fluke meter...$200. Ask me how I know.....lol. Bones
Your right, there's nothing a light can do that a meter can't do. Some guys don't have meters and the most common test to check fuses is a test light. The issue I had was rear seat fan motor wasn't running so I did a quick check with my home made headlamp test light. It lit on both poles of the fuse in place, some guys would than go elsewhere thinking the fuse was good. It wasn't until I pulled the fuse that I found the fuse corroded past the filament causing an open. Yes, a meter would have shown source voltage. Either way, I still would have pulled the fuse to perform visual inspection. The reason I use a headlamp test light is I got burned diagnosing an ABS light. Flow chart/schematic said to test power at EBCM motor control circuit at the EBCM. Meter showed source voltage and advised to replace the EBCM. It didn't fix it and created a shit storm with writer and customer. I then went to the fuse block and used my meter to double check voltage at the fuse, it showed source voltage. I then used the headlamp to check the fuse and it lit dimly, the circuit couldn't handle the 8-10 amp draw from the lamp. As it turned out, there was a few of fuses in the block that did the same thing. Turns out the BEC ( bussed electrical center ) was bad. That's why I will never give up my headlamp test light. As far as the ones with the tiny bulb? I'm with you.....CHUCK IT, 'cause it'll burn ya too!! I got burned once before for not pulling the fuse once before because of the same thing, the open was AFTER the filament in the "leg" of the fuse. I just want to lay out some info for guys that freak when confronted with electrical issues. I still use the headlamp because I got burned when the meter sent me in the wrong direction. When I left GM, they changed all of their diag procedures so you had to use THIS: http://www.ohmslawcalculator.com/ohms-law-wheel for all of your circuit testing; they wanted to know what the computers actually saw and it became VERY time consuming to be getting paid only warrantee times.....that's one of the reasons I rolled, they wanted us to do too much and not pay us. Sorry for the long post.....hope things are a little clearer now.....
No that makes more sense, I was at work and didn’t read properly. My advice although off topic is no test light with computer circuits, poking around with a test light puts it in parallel with the circuit, total amperage goes up can have a very unhappy module....part of the reason I dislike test lights! It’s hard to get this stuff across in texts, I spend two weeks of class time with students to go over this stuff! Sent from my iPhone using H.A.M.B.
Oh! I totally agree on late model stuff, where you need to know if it’s 3.7 or 3.9 volts and you need a meter that is made for computer circuits. Some old multi-meter testers , will mess up a computer circuit. ( I think they call them low impedance, or something like that) Here on the HAMB, we kinda talk about the old days and old ways. Back when the test light was king! Lol Bones
Oh yeah....meter only on reference and data circuits......NEVER a test light when diagnosing a computer control or reference circuit........EVER!!!
Hello, From the time I started driving the 58 Impala, I always carried spare fuses. These were the simple glass tubes with the metal contacts on the ends. There were several power ratings that had their places in the fuse box under the dash. The newer u-shaped push/pull blade fuses came much later. 1958 Lions Dragstrip entrance There was nothing worse than to get in your car and have a fuse blown for some reason or other. These small fuses came in their own slide out containers that looked like a Bayer Aspirin size container. The only thing we had to remember was not to break the glass tubes or drop the fuse. The super thin wire inside was very delicate and easily broken. The later versions came with a thin flat metal strip that looked like dog bones inside of the glass tube. They were stronger than the skinny wires. After a few hard runs, it is/was disheartening to be sitting in the pits wondering why a new HD battery would not even turn over the Impala’s 348 motor to get to the staging area. Wasn’t it the purpose of having all of that cranking power? But, come to find out, something made the thin wire fuse blow, sending a couple of teenagers in a tizzy about what was happening. Why wasn’t the motor starting? Then it was the mad rush to go down our check list to eventually find out there was a thin wire fuse that had a split in the middle, inside that glass tube. Jnaki Elsewhere, if we were in the car sitting around listening to the radio with the motor off, sometimes the fuse splits and the car would not start. It was embarrassing when that happened. But, after having a box of fuses, it never happened again. One thing that was “shaky” on any fuse replacement, trying to get those glass tubes out without breaking them. At the drags, when we found out it was the fuse, it was a mad rush to get it out and a new one from that sliding fuse box put in correctly. A flat head screwdriver was always the tool necessary, but you did not want to touch anything for fear of another short. So, those flat wooden ice cream sticks were the order of the day. They went into the area with ease and out popped the split wire (broken) glass fuse. No fuss, no bother. Later on, some company made those plastic handles with a glass fuse size “C” shape on the end, just to get to the fuse. We tried those and failed, so reverted back to the wooden ice cream sticks.
The Jalopy Journal
