How to Install an Alternator in 10 Steps

An alternator.
  • 1-2 hours
  • Intermediate
  • 50-150
What You'll Need
Combination wrenches
Socket wrenches
Vise grips
Large, flat-bladed screwdriver
What You'll Need
Combination wrenches
Socket wrenches
Vise grips
Large, flat-bladed screwdriver

If it’s about time to replace your car’s alternator, you do not have to spend a lot by bringing your car to a shop. This guide should just be a supplement to the steps of installing a car alternator, depending on car brand and make.

One important thing to do is to make sure your car’s engine is cool enough to work with or you could burn yourself. Cover your car’s fender to protect your paint job. Take note that if you cannot locate the alternator, reach the attachment bolts or free the nuts, stop and let a professional technician handle the job.

As soon as you’ve figured out your alternator’s location in your car, note how it is attached to your engine. There should be two points where the alternator is bolted to the engine, one which allows the alternator to swivel or swing in order to vary the tension on the V-belt. The other is usually a curved bracket with a long slotted hole in it that limits the amount of swivel and locks the alternator in place. With either a socket wrench or a combination wrench, make sure you are able to reach the bolts.

In many cases, you must use two wrenches, one on each side of the bolt in order to loosen it. It is beneficial to have another running vehicle close by. Ideally, you should remove the old alternator and V-belt from your vehicle and take them to the parts counter. This way, you can ensure that the replacements match perfectly.

Step 1 - Disconnect the Negative Terminal of the Vehicle's Battery

If you don't do this, some of the wires that run to the back of the alternator can short out if they touch the car body or engine. Disconnecting the battery will protect you and the electrical circuits of the vehicle.

Step 2 - Loosen the Two Bolts that Hold the Alternator

If these bolts have nuts on the opposite side, you may have to use two wrenches on one or both of these bolts. Do not remove the bolts yet.

Step 3 - Rotate the Alternator

Once you have loosened the bolts, try to rotate the alternator to loosen the slack in the V-belt - rotate it towards the direction that the V-belt runs. Just move the alternator enough to remove the V-belt from the alternator pulley. If you are replacing the V-belt at this time, take the belt off the rest of the pulleys on the engine. This may take some patience and involve a couple of scratched knuckles. You may have to work the belt over the radiator fan and shroud.

    Step 4 - Remove the Electrical Wires

    Sometimes they are held in place by plugs with wire retainers; some are held on with nuts and washers. Using the masking tape and marker pen, mark the location of each wire that you remove so that you make sure to install them in the same place on the replacement alternator.

    Make a diagram of the wire locations on the back of the alternator and write down the color of the wire or plug that goes to each location. Check that the replacement alternator has the same type and location of fittings for the wires. You may have to use the old nuts and washers on the replacement unit. If so, clean them and even give them a quick wipe with some fine sandpaper.

      Step 5 - Adjust the Bolts

      Loosen the bolts that hold the alternator in place and remove them. Remove the alternator and set it aside. Take the replacement alternator and, if not already done, feed the bolts into place within the alternator housing. Position the alternator so that you can start to feed the bolts into the holes on the two engine brackets.

      Loosely place the nuts and washers on the back of the bolts. Make sure that you position the loosely held alternator so that it won't swing down and hit your knuckles.

      Step 6 - Install the Belt

      Install the new V-belt on the engine pulleys first (and on any other engine accessory that it drives) and finally, on the alternator pulley. If the new V-belt is not the right size you can temporarily re-use the old belt. You can visit the parts counter again to get the correct size and install a new V-belt at a later time.

        Step 7 - Position the Alternator

        Now you need to position the alternator in the correct place and begin to get the right tension on the V-belt before you tighten the bolts that hold the alternator in place. This can be frustrating, particularly if you are working alone, but there is a way to simplify the job. First, hand-tighten the bolt/nut that holds the alternator to the engine (you still need to rotate the alternator to the correct position on the slotted bracket). Then rotate the alternator until it is holding the V-belt in place with no obvious slack.

        Now take a pair of vise grips and adjust the jaws so that they can tighten on the slotted bracket. Position the vise grips on the slotted bracket just behind the "ear" on the alternator housing. In other words, let the vise grips be your extra set of hands holding the alternator against the V-belt in the proper position. In effect, you are using the vise grips as a "stop" on the slotted bracket.

        Step 8 - Move the Vise Grip

        By just moving the vise grip slightly you can now add the right tension to the V-belt. First, as noted above, make sure that there is no discernible slack in the V-belt. Then pull the alternator about 1/2 to 3/4 inch further in order to pull the V-belt tighter (or, stated another way, apply about 20 pounds of force against the belt).

        With the alternator now held in this new position, reposition the vise grips on the slotted bracket to hold the alternator in place. At this point, you can take your time and tighten all the bolts that hold the alternator in place.

        Step 9 - Remove the Vise Grips

        Remove the vise grips and replace all of the electrical wires on the back of the alternator. Use your wiring diagram as a reference. Re-connect the battery negative terminal.

        Step 10 - Test the Engine

        Taking all appropriate safety precautions, start the engine. First, ensure that the ignition warning light in the instrument panel goes out after the engine has been started. Then listen to the belt. If you hear any belt squeal, the belt is too loose. Shut off the engine and try to further tighten the alternator on the slotted bracket. Be careful not to over-tension the belt. Too much pressure on the engine accessories can ruin the bearings of the water pump or alternator in a relatively short time.