Summary

Chasing a short circuit can quickly turn into a headache. Learn a simple diagnostic trick that can help you find the fault faster without blowing fuse after fuse.

00:00 Hey everyone, welcome to today's webinar.
00:02 We're gonna be chatting about short circuits today It can be a bit of a tricky one to find and a bit of a troublesome electrical problem but I've got a bit of a quick simple trick that I learned a long time ago in my apprenticeship and It's really helped me a lot along the way and gotten me out of some pretty tight jams as far as trying to diagnose something Especially in a timely matter if you're doing this kind of thing professionally Obviously, trying to diagnose things as quickly as possible is key But when it's your own car, you know, you can spend as many days as you want But it's still nice to have those little tips and tricks up your sleeve so, on the bench over here, I've got a Setup is just a generic fuse box that I found and did some very very quick wiring a bit messy But you know, that's generally where problems arise And I've just got a 12-volt power supply that is pairing up a few circuits here But one of my circuits has actually blown a fuse So, in a real-world situation you probably find This kind of thing crops up when you're you know, you're driving around, you know, something in your car doesn't work Whether it's the radio, lights Your seat heater vibrator thing, but generally it does come down to a fuse blown fuse or maybe even a You know another problem, but today we're gonna be talking about when that is a short circuit causing a blown fuse So, along the way you will generally go through each of your fuses and Check power either side or visually inspect them or check continuity across the fuses And once you find your blown fuse, where do you go from there? Most of the time we will just or most people will chuck a new fuse in hope for the best Sometimes you're lucky and there's no problem anymore.
01:45 It was a quick intermittent problem that Isn't coming up again and you go about your day But a lot of the time it will instantly blow or even worse be an intermittent problem where you'll drive off thinking it's all hunky-dory and then it blows down the road or when you Launch it over a speed bump a bit too quick So, those can be probably some of the more tricky ones when they're especially intermittent I'm sort of based this problem around a issue that I had a long time ago A car came in that would very intermittently Blow a main EFI fuse which would cut out the ECU and stop the car running altogether Which was pretty troublesome when you're you know you're driving through traffic and all of a sudden your car shuts off and grinds to a halt and You're scrambling around for fuses and trying to work out what's going on And sometimes the the problem would still be there for at least a few minutes, but generally it would go away after a little while A lot of the time these intermittent short circuits sort of lean towards some sort of short to ground in a wiring harness where it's maybe rubbed through or A pin and wire or pin and pin are contacting intermittently when you have vibration going over a big bump that type of thing but it also can get to a situation where Even just a break in the wire is the issue, but that is an open circuit whereas here.
03:05 We're talking about short circuits So, I'll quickly talk about what the difference is between a short and an open circuit.
03:12 I'll draw up a quick diagram here We'll just have Positive negative battery.
03:16 I don't think I've even got that in shot actually let me just move this over Make sure you guys can actually see it.
03:21 Where am I there we go? All right, let's do a little one Battery comes along here to some sort of load resistor and back around we have a complete circuit That's when we have our flow of electricity So, a short circuit is when basically we're bypassing the component in our Circuit, so in this case it would simply be joining the wire from here to here Which because this is our ground side this could be going to our chassis and this wire here could be rubbing through and actually contacting the chassis and That's sort of where the term short circuit comes from we're shortening our circuit We're bypassing any resistance We then end up with a circuit that has very low resistance and this causes a high current draw That's when things burn out, but luckily we have something called a fuse And that is their whole that's the whole reason they're there is when we have these overcurrent situations too much heat that fuse blows and then we actually cause a open circuit Open circuit.
04:24 It's pretty self-explanatory It's just when we have a break in our circuit and it's open so Really, you know our short circuit is actually causing an open circuit in our fuse But it's there to protect from the short circuit heating up our wires and causing problems down the road fires and things like that So, let's get stuck into it and how we can actually Diagnose this with a simple trick before I get into that though.
04:49 I will mention.
04:50 This is a live webinar So, if you guys have any questions wait around to the end and we'll do a Q&A and you can ask some more questions Maybe you have your own examples and things like that.
04:58 We can talk about it If you are watching a later date, I apologize when you ask any Q&A, but jump on the forums and ask any questions there So, let's get stuck into this.
05:08 I've got everything powered up right now And if I get our trusty test light Which is just an LED one get this in a way that you guys can actually see going through my fuses here They're all looking good, so far.
05:19 Good.
05:20 Good.
05:20 Good.
05:20 Good.
05:21 Good Not, so good, so there we go straight away that is my blown fuse.
05:25 That's my problem circuit If I pull that out should be able to visually inspect it and I can say 100% that is blown Mainly because I purposely put it in there blown But in your own situation when you go to your fuses if you check it that way you can go straight to you know You find which circuit is the problem you might already know which circuit it is say a headlight or a Radio and then you can go to your fuse diagram and actually pinpoint which one it is But also testing with a test light does you know gives that confirmation and you can confirm that it is definitely that circuit One of the big problems we have though with that type of thing Especially in our cars is a lot of these circuits actually run multiple components So, say on my fuse diagram for this fuse at the top It's running cigarette lighter, radio, power windows Probably not, but we'll just say it is and maybe a few other circuits So, how do I know where my short circuit is actually happening? And I will I'm not going to go wasting fuses, but we will say that there is a constant short there we can check that by changing our test light over to positive and Because we've created a short where we've Completed our circuit bypassing our component There's basically a constant ground to one side of our fuse and that lights up my little indicator there green if we can see it Telling me that there is a ground there and that's why when we put our fuse across we cause a blow Now, this is where my little trick comes into play and the secret that I learned a long time ago It's probably not a secret to some of you But it just it's one of the handiest little tools that you can make at home and is really good for testing this kind Of thing and helping you out This is a fairly simplified version, but basically what I've got here is just a Normal 12 volt LED globe if you're using if you're in a 24 volt system use a 24 volt globe but all I've done with this one is I've bent my tags out for the filament and crimped on some blade terminals Now, in reality, this is kind of just a simplified version, so I can you know fit it here.
07:30 There's not too many wires but I prefer to get say H4 globe or something with some terminals on it already and something that you can then run quite a length of wire Connect it up put a blade terminal on the benefit of these blade terminals the generic I think they're about a 6.3 mil wide they actually fit into our fuse Fuse terminals themselves.
07:53 We have a look there They're basically the same size and what we can do is actually put them across our fuse So, because we've actually got a short circuit here if I complete that again Because we have a circuit here where well actually I'll leave that break there We've completed our circuit and got a ground in the other side if we put a component in here like a light bulb We've now created another circuit and it's a good circuit We need some sort of resistance in there to limit the amount of current that's going to pass through if We have just a single wire there.
08:23 No, fuse.
08:24 It's going to burn everything up and cause fire and release the genies So, we're essentially just putting in another component and bypassing Bypassing the fuse, so we don't have any circuit protection in here, so I do recommend Being a little bit careful.
08:40 You know when you put your globe in if things get really really hot it You know take it out immediately, but because we're putting in a simple globe I'd suggest something like a 21 watt or a 5 watt.
08:50 We're limiting the amount of current that can pass through So, if I demonstrate that right now as soon as I put this in because we've got an earth one side and power to the other it will Light up So, there we go.
09:04 I can successfully say that there is a short circuit there As I was saying earlier using a globe that has terminals already on it is really handy Particularly because you can run a nice long bit of wire and say you've got your fuse box under the engine bay But your problem is in the car You can kind of wrap that around your bonnet latch or something have it hanging in the air and because it's a light It's really nice and easy to see from wherever you are if you're just putting fuses in and blowing fuses it's really hard to actually find where that short circuit is happening and Then separating it and diagnosing it So, this gives us a really good point of reference to show that we do have a short circuit still So, to actually diagnose this Diagnose this what we actually want to happen if we want that globe to turn off when that turns off That means our short circuit is gone again, this is really handy if you've got an intermittent fault particularly something like a Rub-through harness because you can go around and essentially move your harness tweak things around Try and imitate what happens when your engine is running and you'll see if you have found the area where your short is you'll see your light starts flickering and Joining and disconnecting and, so forth so, when it comes to actually Diagnosing the short in the circuit that I've got here what I have wired up I've basically just wired into some of these fuses going into connectors gone to a few other connectors Made a bit of an imitation small circuit obviously in a car these go all the way You know through the body anywhere and everywhere and it could be a bit of a time -consuming hassle So, to kind of narrow it down, especially when you have multiple circuits off of one fuse What I recommend is For starters having a diagram if you do an electrical diagram Definitely helps a whole lot.
10:46 You can actually trace where each of your power lines are going Sometimes they even go to something that isn't listed on your fuse box and that can be pretty frustrating but what we're basically gonna do is just isolate all our components and just keep narrowing it down until we get that light bulb turning off into a Turning off when we play around with a section that we can obviously see that's where our fault is So, with this circuit here my connector that I have here my Deutsch connector I know already this is my main connector where everything is branching out from so, ideally this should shut off when should shut the light off when I disconnect it and There we go So, basically what that's telling me is my circuit from the fuse from the light bulb at the moment all the way to this connector That is okay.
11:32 If I disconnect that and the light stays on my short circuit is in that section somewhere So, reconnecting that I now know my short circuit is beyond that connector So, yeah at the end of the day, this is kind of a narrowing down thing and process of elimination So, next going through my circuit diagram and looking at what is connected to this I know it's my yellow wire here that yellow wires coming over here.
11:57 That's another component I can't you know, there's no other connectors here, but we do have a screw terminal So, I can undo the screw terminal Take out that blade and we've still got our light on So, what I've done here is essentially isolate everything beyond that and I know that the short circuit is still there So, it is either in this section of wire or on a completely separate circuit Obviously, if it is in this section between here and the connector it can be difficult to find exactly where it is That's where playing around with your wire the harness, you know giving a bit of a wiggle around Generally, finds that kind of fault But I do have another connector over here.
12:40 That is Actually, I got two more.
12:42 Sorry that are the other two circuits in this fault circuit here under here I've got some wires and that might be rubbing on the body.
12:49 But no, it's just disconnected completely Nothing here is the issue can check if I got power here.
12:54 There's not even power.
12:55 Oops.
12:56 Sorry.
12:56 I've got that on positive So, that's actually put that on negative I don't even have power here.
13:02 So, that can't be where my fault is The other one is my connector up the back here.
13:07 And if I disconnect that it's already disconnected.
13:10 So, that can't be my issue either So, what I've done now is isolate everything beyond these connectors this one here a little connection under here to their wire and this one here, so now I know my fault is basically between this connector because we could get it to shut off and Between the other connectors in the circuit, so it's in the harness between these connectors So, this is obviously where it can be a bit frustrating trying to find out where that break is But it does narrow things down quite considerably.
13:39 We do know that it's not a component.
13:41 It's not say a Just an ECU or PDM or something else in our system that is internally short-circuiting and causing the issue We can basically confirm that it is a definite wiring fault and our short is in that loom somewhere So, the next thing as I said wiggling your loom around is a It's a really good diagnostic tool.
14:02 Like it may sound silly, but just moving things around it does, you know, it shows Faults my light has turned off and it turned off when I was wiggling this bit of loom up here See if I wheel it around a bit more our light starts flashing So, now I have at least found the area where the fault is It hasn't narrowed it down completely, but I know that it is sort of in this section here If I move my loom, oh even over here turned off that might have just been a little bit of coincidence because it is moving over There let's sort of go back and forth Yeah, it's mainly when I'm touching over here.
14:34 There we go.
14:35 See that's the real culprit and If I mean, I obviously know where the fault is.
14:39 I did put it in properly If I get this little bit of loom down here, I can move it in and out And it is definitely where our short is That's because I have grounded this plate underneath this metal plate and if I get this bit of loom out here bring it around We can see somehow you might be able to see this in the Camera my wire has actually rubbed through and that's where my issue is quite simply We've you know narrowed it down fairly quickly in this situation just because everything is here and I didn't know where the fault was But having that light bulb really makes it, so much easier If you think this is a fuse box in the car or sorry under the hood and you're in the car Fiddling around with wiring trying to work out where that fault is.
15:22 You can have that light bulb dangling down from your Bonnet as I said or even from your window and you know that will give you a really good indication It's nice and bright, so you can actually see it when you're wiggling things around moving disconnecting You're not constantly going back to a multimeter and checking that type of thing.
15:38 I Will say though you do need to be a little bit careful and use your brains a little bit The light bulb will get hot don't obviously lay it on you know plastic or things that are flammable that type of thing keep it You know nicely tied away, but well in view that you can actually use it So, that is a quick and simple way to diagnose these short circuits and obviously to fix this fault We need to rectify that short that open wire either replacing the full wire or just that section that's going to rectify that we can then come back to having our globe in there and Say I fix this we put it back mount it where it's supposed to be and the globes off that is good globe off means No, short Obviously, we also want to prevent this from ever happening again.
16:23 This was pinched under my fuse box and the plate So, I'll make sure that that wire is secured where it should be and away from those pinch points now, that I have rectified the fault our globe simply comes out into your toolbox to be used another day a Good fuse not the blown one that I've had before that goes in and happy days.
16:43 We've fixed our fault and No, longer have a short circuit So, that is it's a quick and short one today But that basically shows you a really good method that I learned a long time ago as I said and it has absolutely saved me like I said I based this off of a Job that I had a very long time ago car came in that was intermittent fault driving around And basically it was in the main loom There was a slight rub through on the harness and I did exactly what I did here Separate as much components as I could basically found the midpoint of where I could disconnect get the light to turn off Disconnect at the other end and the light would stay on telling me that the fault was in there And then it was just a matter of wiggling that loom around and I could actually find where that light would then Illuminate when I was moving around and saw the loom was rubbed through onto the engine block causing our short and causing our intermittent fault something that a lot of other people had looked at previously and couldn't find it purely because it was, so hard to Try and get it to refault a lot of the time people would replace the fuse drive the car around no issue Everything was all good didn't go on bumpy enough roads of roads Obviously, I didn't give it a good wiggle around and would come back saying look.
17:55 It's fine now There's nothing we can really do about it When it comes to electrical and diagnosing Replicating the fault is the biggest thing if you can't replicate that fault You really can't find the the reason for that fault and yeah, yeah, unless you have the actual symptoms You're not going to find that fault Now, so there are other methods there are specific tools designed around this But I just wanted to show you guys this one in particular because it is such a cheap and easy method you can Rip a globe out of one of your mate's cars or just go buy a cheap one Chuck a couple of terminals on there stick it into the fuse and away you go Obviously, there are some fuses that are different sizes.
18:35 We have our mini and micro fuses that type of thing What I sort of would do is have a globe with terminals Maybe a connector and then other wires with different types of terminals, so you can mix and match and basically make it work How you want it? Hopefully, that's given you a really good idea of you know How to now find a short circuit in the future find it yourself not rely on someone else And have a little tool that you can chuck in your toolbox and have on hand for those pesky days It is also a really good one that you can even just make out of the blue Don't have to have a terminal in there if you're really in a pinch You can just you know wrap a bit of wire around make it touch those two terminals and get the component to light up Now, also using maybe like an LED that obviously gets rid of things like having too much heat or drawing too much current That will be the next thing Also, if you're using a globe that's say like a high high beam globe That's a hundred watt that will draw a fair amount of amps like around you know Anywhere from six to ten amps, so make sure that the circuit is suited for that easy way to tell Whatever fuse is in there from factory.
19:40 That's sort of what the circuit is designed for If you have a 5 amp fuse in there Don't go running a really high watt globe to check that fuse because you're gonna be drawing too much current than what that circuit is Actually, rated for and that's kind of why that fuse is there too Was originally there to stop that kind of thing happening So yeah, you are bypassing a safety feature.
20:01 So, be careful and be sure that you are using a Correct wattage globe, but generally just going for something low wattage 21 5 watt Just something that it lights up when you put it in there That's going to be happy days and it will because it's our new essentially a resistance in our circuit It's gonna limit the amount of amps that can actually go through So, that's that's been a really quick unfortunately, but hopefully you guys maybe have some questions We got no questions.
20:30 I really don't want to keep it this short though.
20:33 So, what else can we talk about? It's basically covered short circuits they are Well, they are a pesky problem and hard to diagnose.
20:42 Sometimes it really just comes down to my biggest tip is Isolating circuits.
20:49 So, as you saw disconnected connectors, it's not just your connectors in line Disconnecting components themselves.
20:55 So, say your EFI fuse is blowing Disconnecting your ECU making sure that that isn't actually the problem You could have a short circuit internally in your ECU causing that kind of issue You can diagnose the same way And that would actually, you know, you disconnect your ECU You see your light go out and then you'd be able to say that that is your problem on that though Be a little bit careful because you do have circuits that go into your ECU and then out onto other circuits other components so, it could just be going through the ECU and then essentially breaking contact because you're disconnecting that circuit that goes through the ECU Maybe a bit of a convoluted way to say it, but yeah Don't go replacing an ECU just off the top of your hat just because yeah You disconnected it and that circuit goes away Trace it through the ECU, see where it goes, make sure it isn't anything further down the line Really, I think that pretty much covers what I wanted to talk about I really hope it has given you guys some sort of extra tool for your Diagnostic basket.
21:58 Diagnosing electrical is I think it's one of the hardest parts for electrical Anyone can hook up a light or two, but actually diagnosing a problem really separates a good electrician from not, so good So, if any more questions, unfortunately none at the moment Which I guess is good means I've hopefully covered everything as much as I should If you are watching this at a later date and you have questions or you don't quite get your question in time now Jump on our forums.
22:24 Make sure you get them in there and we can answer them or on to our support email We're here to help you guys and answer those questions Also, if you've got any ideas for future webinars, things you want to see, something you want us to dive into a little bit deeper let us know in the comments, the The chat, email, forums, everything.
22:43 Have a great day guys, and I hope you enjoyed this.