Solving Automotive Electrical Problems
This section is split into different parts, starting with coming up with a plan. I can’t cover all contingencies here, but I’ll do my best to cover the basics to give you an understanding of how to go about solving an automotive electrical issue.
As mentioned above, you will have a much better chance of success if you have a plan going into an electrical problem. Here’s what I normally do when dealing with an electrical issue.
First, a good inspection. I start at the battery. If it looks old or corroded or has loose terminals, I deal with that first. I know not all electrical issues are the result of battery issues, but considering its importance in the electrical system, it’s worth at least a glance when you open the hood. If you suspect an issue, check the surface voltage, load test it, clean up, and deal with any battery terminal issues you might have.
Next, check all the fuses — and I mean all the fuses. I can’t tell you how many times I’ve fixed an electrical issue just by replacing a fuse. If that same fuse continues to blow, you need to look further into that. Most times if there’s a recurring problem, the new fuse will blow almost as soon as you put it in. If it doesn’t, activate the affected system and check its operation. If it’s good, monitor it until you feel confident it’s not going to have a problem again.
If you do have an electrical problem, find a wiring diagram for the affected circuit. Without it, you’re lost. The best wiring diagrams, in my experience, are put out by the manufacturer. Do what you can to get your hands on one of those when dealing with an electrical problem.
Once you have the wiring diagram, study the circuit. See if you can figure out what the issue is before you even go to the vehicle to do your testing. It is possible to do this with a bit of practice and the ability to read a wiring diagram. Sometimes you can look at the diagram, find related circuits that might be affected, test those, and find the problem through a process of elimination. This is really where your plan gets put to use.
I like to start at the load when checking for electrical problems, especially with 12V systems. I do this especially if the load is easy to get to. What I mean by load is the component(s) the circuit controls. In the case of a cooling fan circuit, the cooling fan is the load. All the other controls of the circuit are there to control the operation of the fan, or load. I do this because I often find it’s the load itself that’s failed. I also do this because the load is sometimes more accessible than the wires or controls going to it. I can unplug the load and check for power and ground to the component.
If I don’t have either one of those, I know where to go next. If I do have those, I check the operation of the load itself. If it’s a cooling fan, I run power and ground directly to it to see if it can operate on its own. If not, I know it’s bad and I can replace it.
If it does work, I’ve got more investigating to do. Sometimes you can have power and ground in a circuit and it’s not enough to work the load. This can be due to a short circuit or increased resistance in the circuit somewhere. Once again, we go back to the wiring diagram to try to figure out where that might be and come up with a plan for testing the suspected part of the circuit.
Once you’re done finding and repairing the problem, verify your work. Make sure everything works like it’s supposed to. This way, you can avoid having to deal with it again in the future.
In the simplest terms possible, I’m going to cover the basics. The first thing to know is that all the electricity in an automotive system begins and ends at the vehicle’s battery. This is the heart of the system. If you don’t have a good battery and perhaps the voltage is a bit low, everything else in the vehicles electrical system will be effected.
Don’t rule out engine performance issues here. Your vehicle’s computer speaks in the language of voltage. If it doesn’t see proper voltage signals or doesn’t have enough voltage to run properly, everything will be affected. This is especially true with newer vehicles that rely on a lot of electronics. Electronics, especially computer-controlled electronics, are very sensitive to voltage changes, especially low voltage. If they don’t have enough voltage to operate, they tend to act strange, or, in some cases, even fail.
My point: When dealing with any automotive electrical issue, start with the battery. Check its voltage and its state of charge. A good battery should have at least 12.6V for a static charge. It should also be able to pass a load test and stay above 9V when placed under load. Here are two videos about checking an alternator and a starter on a vehicle where you can put this knowledge to use.
Before we’re finished with the battery, let’s talk about one more thing: connections. I would wager that about 90% of electrical failures are the result of poor or inadequate connections. In addition to checking the battery, also make sure you check its connections and cables. I’ve seen my fair share of electrical problems caused by bad connections. If you have a lot of corrosion at your battery terminals or the terminal isn’t tight to the battery, this can cause an electrical problem. Clean and tighten the battery connections and recheck for your electrical issue if this is what you find. Here’s a video to help you out.
After making sure your battery is good, the next step is to check all the fuses. Notice I said all the fuses, not just the ones involved in the circuit that’s having a fault. On more than one occasion, I’ve found a good fuse for the affected electrical system I’m trying to repair, and another fuse that seemed unrelated that was blown, which was the problem all along. It’s worth checking all the fuses if you have an electrical failure. Nothing is more frustrating than tearing an entire vehicle apart looking for a problem in a wiring harness only to find that it was a blown fuse the whole time.
Lastly, don’t forget about the large fuses that might be physically attached to the fuse box. Say you have a no-start condition, perhaps after attempting to jumpstart the vehicle. If the cables get hooked up wrong, it will normally blow one of these main fuses. So if you have a vehicle with no electrical power at all and a good battery, check the main fuses. You might find one that’s blown.
Would you go on a long road trip to someplace you’ve never been without a map or, at the very least, some directions? Probably not. The same is true for electrical problems. Don’t get into an electrical diagnosis without a wiring diagram. It will take longer and perhaps cause you a great deal of frustration if you don’t have a wiring diagram for the circuit you’re working on. A wiring diagram is the roadmap for a particular circuit. Without it, you’re lost.
I realize that if you don’t know how to read a wiring diagram, you’re in the same position as not having one. If that’s the case and you’ve checked all the basics and still have an electrical problem, perhaps it’s time to take the issue to a professional. It might seem expensive up front, but in the end, you might find that you save a great deal by not pursuing the problem yourself.
If, however, you do know how to read a wiring diagram, do your best to get your hands on one for the circuit you’re working on. It’s not often you find these online for free; you normally have to pay for them. BBBind.com has some free diagrams you might find helpful.
Once you’ve found the diagram and have studied the circuit, try to come up with a plan for testing that can yield you a result. With an understanding of the circuit and a good idea of what the issue might be, I’m sure you’ll be able to solve the problem in a reasonable amount of time. If you go in blind, expect it to take a lot longer, and the results might not be what you expect.
Relays are used throughout automotive electrical systems. The purpose of a relay is to allow a low-amp circuit to control a high-amp circuit. Relays are just electronically controlled switches. You might find that one relay contains multiple relays inside it. This is common in modern systems. If you’re lucky, a wiring diagram and terminal label will be printed on the outside of the relay. This will make your life much easier. If not, try looking for terminals of the same color. This normally means that they are part of the same circuit. This information might not always work for you, but it’s done well by me for years now.
There are two basic parts to a relay: the coil and the switch. The coil is the control circuit and is used to activate the switch. It does this using the electromagnetic principle. Once the coil is energized, it creates a magnetic field, which closes or opens the switch. That’s worth mentioning here. Some relays are normally closed and the activation of the coil opens the switch instead of closing it. This is where your wiring diagram comes in handy. Testing is fairly straightforward. Just activate the coil and check the resistance of the switch circuit. This video will help explain it.