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Saturday, October 8, 2022

Fuse tab || Fuse box

Do you want to connect a fused circuit from your vehicles fuse box? Do you want to power an auxiliary device like a dashcam or power socket? Want it safe, reliable and with clear and simple instructions? I’m going to be looking at adding a fused circuit directly from the fuse box of vehicle to safely power any auxiliary device. Here we will discuss about Fuse tab || Fuse box || how to connect or repair car's fuse box. Fuse tab is used for tapping from fuse to headlight/bulb in any equipment/device like car. You can see cars fuse box under the steering wheel. I’m going to be using a plasticine fuse board and a few helpful diagrams to make this really simple to understand.

Fuse tab || fuse box


How to connect or repair car's fuse box?

It’s much easier and safer to use a piggyback fuse which provides a secure, reliable connection and a fused outlet. Here is the makings of a very simple circuit – a battery and a lightbulb. To make the lightbulb work, we have to connect it to the battery using wires whereas one wire to the positive battery terminal and another wire to the negative. There was light So now we can imagine that the electrical current is flowing around the circuit. It’s going from the positive terminal of the battery, the red wire into the lightbulb and the blue/black wire back into the battery. 

In case of a vehicle, these things aren’t quite the same. We have a battery and a lightbulb but the wiring will be a little different. Ignoring switches, fuses and relays, etc, to power the lightbulb, We need to run a wire from the positive terminal of the battery to the headlight. But in the vehicles, rather than run a negative wire, manufacturers use a shortcut i.e. use car body as negative terminal. As the vehicle body is made of metal and it conducts electricity, the negative terminal of the battery is simply bolted to the chassis so to complete the circuit, all we need to do is connect the headlight to the chassis of the vehicle. It now has both positive and negative supply so electricity will pass easily and bulb will glow which also means that the electrical current can flow from the battery to headlight and that mean the headlight will work. For wiring connection, we can use fuse tab for it which is easy to connect.

How to connect or repair car's fuse box

The process of connecting negative terminal to the chassis in vehicles is often called earthing or grounding. Once you understand this idea, you can make more sense of vehicle electrical circuits so let’s look at our simple lightbulb circuit again but this time we’ll introduce a fuse. The fuse is a necessary safety item that protects all the electrical devices, so don’t ever try to short these out with wires or tin foil. Of course the fuse needs a fuse holder and as you can see from this diagram the fuse is not plugged into the holder so the current can’t flow. But when we plug the fuse into its holder, we complete the circuit with easy connection with fuse tab.

There’s an IN and an OUT on the fuse board of your vehicle and you’ll need to find this. I’d recommend using a multimeter for this purpose, For that set it to Direct Current (DC) Voltage, in the lower range. With the fuse pulled out, we can determine the IN and the OUT but in your vehicle it might not be so simple. Don’t assume, you need to test it first. Place the black probe of the multimeter onto the chassis of the vehicle, maybe a nearby bolt or screw, remember that this is the negative connection. The positive probe can be placed against one side of the fuse holder. You can see the measure voltage that will be about 12 volts as that’s a typical vehicle voltage. To confirm this, move the red positive probe to the other terminal of the fuse holder, you will find that others measures will be zero volt because there’s no current flowing through it as there’s no fuse. If there was fuse, we will obviously get 12 volts, so remember the fuse MUST be pulled out. There’s lots of different colored fuses of different ratings, and that doesn’t matter. Our first job is to discover which way the power comes IN to each fuse. So let’s pull a fuse. In your vehicle, you may find it helpful to use long-nose pliers. Gently grip the fuse as too much pressure will crush it and then just pull it upwards. We can now use the positive probe to check for the IN and OUT by inserting it into the hole left by one of the terminals of the fuse.

Fuse box || How to connect or repair car's fuse box


If one registers 12 volts, that’s our IN. From now on, we need only take our measurements from this terminal. The other terminal will register zero volts. But what if they both register zero volts. That is possible and highly likely because some of these fuses will be permanently on – permanently live and others will only be on when the vehicle ignition is turned on. It’s important to differentiate between these Permanent INs and Switched INs as it will have an effect on the device/car for example a dashcam needs a switched supply. Otherwise it would be operating in when the vehicle was empty. An intruder alarm, on the other hand, would need a permanent connection as it would be pointless having an alarm that was only active when you were driving the vehicle so have we found a permanent IN here, a permanent live connection? With the ignition turned completely off, if any probe registers a voltage of 12 volts, this must be a permanent live. So let’s try another fuse with similar way.

With another fuse removed and the ignition completely off, we can measure the voltage on the IN terminal which registers zero. But if we turn the ignition on, we can see that the voltage is 12 volts, so we’ve found a Switched fuse, perfect for a dashcam or similar item. It’s very easy to connect to the wrong sort of fuse, so taking your time to determine which is Permanent and which is Switched is critical for the correct function of your devices. Typically the inside cover of your fuse box will have a diagram showing which fuse is for which electrical item in your vehicle. This should help you cut out the guesswork and let you make an initial educated guess as to which fuses will be permanent and which will be switched.

Once we’ve determined which fuse we’re going to use, it’s simply a case of replacing it with the piggyback fuse holder. Some people argue that you shouldn’t use a piggyback fuse on just any old fuse, especially if it’s for a safety item like airbags. I’ll leave that decision to you. Personally I think that anyone having that opinion just doesn’t really understand how a piggyback works. It doesn’t affect the original fuse in any way. It simply extends the original fuse holder and incorporates a second one. If you look closely at the piggyback, you can consider the bottom section to be a simple fuse holder. This is where you’d plug back in the original fuse. It lets current flow through it just how you’d expect a fuse holder would. If we look at the upper section of the piggyback, we can see a little different. For starters, it has a red wire trailing off it. The upper holder shares the first terminal with the lower holder. This is the section into which the fuse for the NEW circuit needs to be placed. You can see how the current flows from the first terminal, through the new fuse, and out through the red wire. It has no affect at all on the lower fuse.

It’s very simple to insert the piggyback. Once the original fuse is inserted to the bottom holder and the new fuse to the top, it’s just a matter of placing it back in the fuse board where the original fuse came from. The piggyback holder creates a new, secure, fused circuit. All that remains is to extend the red wire from the piggyback holder to the new device. These piggybacks generally come with one of these crimp fittings attached. You can also use a new fuse tab for it, for that you can buy online ot near workshop. You simply insert the wire into the connector, squeeze it with a crimping tool and the wire is extended or you can cut these and solder a join, but either way you now have a live, fused feed which you can attach to your chosen device. And as you’ve discovered, you can usually get a negative connection nearby on the vehicle from a handy bolt or screw.

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