What Causes the Alternator Fuse to Blow?

The car’s alternator fuse – usually a fusible link or wire in the fuse box under the hood on the passenger side near the battery plays an important role in protecting the alternator in case excessive and damaging currents are being drawn from it.

This fuse is usually rated about 100 A or higher.

How can you tell that the alternator fuse has blown?

What even causes the alternator fuse to blow?

In this post, I share the common reasons why the alternator fuse might blow, and what signs show whether it has blown.

Quick Answer: If your alternator fuse blows then there is likely a short circuit possibly the alternator output is connected to the ground.

This might be at the alternator itself or along the cable connections to the battery.

You can do a visual inspection of the cables from the alternate for any signs of damage and use a digital voltmeter to conduct a continuity test.

If unsure or you have any safety concerns consult a qualified auto mechanic for assistance.

Reasons Why your Alternator Fuse Might Blow

If your alternator fuse is blowing, check any of the following:

#1. Inspect the alternator output cable connection

Have you recently replaced the alternator? If so, it is possible that the output cable connection to the alternator stud has not been fixed properly and is shorting with the casing.

Inspect the connection point and confirm that it has been properly connected.

#2. Short-circuit along the alternator output cable length to the battery

Additionally, there might be a short further along the cable length between the alternator and the battery. Perhaps it is a case of melted cables shorting. Inspect the cable along its length for any signs of cable damage or exposed cables, short-circuit and fix or replace the cable.

#3. Reversed polarity

Accidentally reversing the battery connections – usually when installing a new battery can also short out the alternator fuse.

The positive battery cable should be connected to the terminal of the battery with a “+” sign and the negative to the terminal with a “-” sign.

As simple as it seems, it is possible to make a mistake if in a hurry or when tired.

#3. Faulty alternator

A faulty alternator possibly faulty regulator, diodes, or windings can also short out the alternator fuse.

For suggestions on how you can pinpoint the fault to the alternator, check here.

Where you Can Find the Alternator Fuse

Is there a fuse for an alternator?

In most cars, there is a high amperage fuse that supplies electricity to all the other fuses and subcircuits and the battery.

Usually, you can access the alternator fuse by checking the fuse box under the hood on the battery side.

Depending on the make of the car, you might need to remove the fuse box and undo the screws that hold the fusible link under the fuse box. Consult your car’s owner manual.

If this fuse is blown then the subcircuit and battery will not receive power from the alternator.

Tips to Prevent fuse from Blowing

Make sure you install the alternator output cable properly so that it does not touch the alternator case when replacing an alternator.

Also, double-check cable markings when connecting battery cables to avoid accidentally reversing the polarity of the cable connections.

Note, these signs are not conclusive – they may be caused by other faults

Signs that a Car has a Blown Alternator Fuse

if your alternator fuse has blown then, you may see the battery warning light and the car battery will stop charging.

Note, this sign can also point to other faults – bad battery, cabling, and or weak cable connections.

If you suspect that it is a fault with the alternator, you can replace the alternator fuse.

First, disconnect the alternator and connect the battery. If the fuse blows again, then you know that it is with the wiring or the car battery.

You may also be interested in the post: Why the car battery light is on yet the alternator is charging

If it does not blow, then likely there is a problem with the alternator.

You can have the alternator independently tested at an auto repair shop.

You may also be interested in this post: The common risks you face when you drive with a bad alternator

Why your Alternator’s fuse may Keep Blowing?

This is likely because the underlying fault is still present and not fixed. Inspect the alternator cabling for any signs of damage.

Check out the section on possible causes of fuse blow.

Will a bad Alternator blow fuses?

Yes, a faulty alternator can cause the alternator fuse to blow. An example is when the voltage regulator, shorting diodes, or windings are shorting.

Either of these faults can cause the alternator to generate high currents that blow the fuses.

Will a Car Start with a Blown Alternator Fuse

Yes, a car can start with a blown alternator fuse provided the battery has sufficient charge.

During the start, the car relies on the battery to provide starting power.

However, the alternator will not be able to charge the battery therefore the car will not be able to start as the charge is not being replenished.

Final Word

If the alternator fuse keeps blowing, then you likely have a short-circuit.

Possibly the alternator output is grounded somewhere.

Other possible reasons why the fuse will keep blowing are a faulty alternator, a bad connection at the alternator output that is touching the case, or even shorting cables from the alternator to the battery.

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