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How to Wire an Alternator in a Classic Car

How to Wire an Alternator in a Classic Car

Posted by Jay Johnson on Nov 18th 2021

In the mid 60’s, as electrical demands increased along with the introduction of air conditioning alternators replaced the generator. Alternators - unlike generators - produce more power for the size and weight and will keep batteries charged at low speeds and idle.

Alternators come in both 6 volt positive and negative grounds and 12 volt negative ground versions, and are great upgrades to any classic to power the numerous electrical demands of today’s classics and will keep the battery charged.

The following guide provides a few details you need to install a new alternator and correctly wire it into your classic automobile.

About Vintage Alternator Installations

Alternators are configured in 1 and 2 wire connections: The 1 wire alternator only requires one wire from the alternator output connected directly to the battery. It’s very simple and works good on new, faster idling engines with correct pulley ratios to spin the alternator fast enough at idle.

The 2 wire alternator utilizes 1 additional connection to a switched voltage source to excite the field coils. In this configuration the alternator will charge the battery at all engine speeds and this is why 2 wire alternators are recommended for most conversions from the old generator to an alternators.

The other feature of 2 wire connections is the ability to operate charge/no charge dash lights. These lights became popular in the 60’s when auto makers dropped the battery gauges in favor of the dash warning light.

For purposes of these discussion, all alternators we are working with are internally regulated and do not rely on external voltage regulators.

What You Will Need to Install an Alternator

Our instructions apply to 2 wire connection alternators running on either 6 or 12 volts. The most common of these alternators for vintage cars as follows:

Delco 10si Alternator - The 10si became popular in the early 1980’s and comes in 12 volt 63 and 100 amps or 6 volt 50 amps and will accommodate 3/8” 5/8” and 3/4” wide pulleys

Delco CS130 Alternator - The CS130 is a latter series alternator and comes in 100,160 and 220 amp with advanced cooling and all ball bearing. These will also allow 3/8” 5/8” and 3/4” wide pulleys.

In addition to the alternator itself, you will need the correct size output wire, fuse, exciter plug along with the correct alternator bracket to adapt to the engine. The 2 wire alternator plugs are specific to the type of alternator. The 10si alternator needs a P10Si plug and the CS130 a DSC130 plug. Both these plugs snap into a connector on the back of the alternator.

Steps to Install an Alternator

1.Disconnect the battery before doing any work involving electrical keeps you and your vehicle safe.

2.Remove the old generator and tape back or remove the ARM and FLD wires going to the voltage regulator. Modern alternators come with internal voltage regulators and you will no longer need the old voltage regulator.

3.Install the correct alternator brackets for your engine and mount the alternator to the bracket.

4.Place the belt over the alternator pulley and tighten it until you have about 1” to 1 ½” of belt deflection. Depending on the original set up, you may need to buy a new belt for this if the new alternator has a significantly different arrangement.

5.Install the correct exciter plug for the type of alternator. It should snap into place in the rear of the alternator.

6.Connect the red sense wire (on 10si alternators) to the output stud and the long white excite wire to the positive side of the coil, or to the key switch. (in negative ground systems)

7.Connect one end of the red 10 AWG wire to the output stud, over the sense wire if present. The other end will connect to the amp meter, cut to size. Use the cut piece to attach the other terminal of the amp meter to the positive side of the battery, start relay, starter, or start solenoid depending on your setup. Do not connect high output +100 amp alternators through the old dash battery or ammeter, these were designed for 30-40 amps only. recommend aftermarket volt meters.

8.Reconnect the battery and charge to 12.6 volts. Don’t assume that the new batteries are fully charged. Double check that the Positive from the alternator output  (neg grd systems) is connected to the positive side of the battery and the alternator itself is well grounded back to the neg side of the battery.  If either is not connected or grounded correctly damage will occur to the alternator internal regulator.

9.Start the vehicle to test. Output voltage should be 14.1 volts +/-. If a meter is not available you should be able to hold a pocketknife or screw driver against the back of the alternator bearing and feel a magnetic pull tell that the alternator is charging, best to use digital voltmeter to test.

10.You can also get an up close look at how to connect the plugs, excite wire, sense wire (if applicable), and charge wire to either a 10si or CS130 alternator in this video see link below.

Download our FREE guide how to convert any American Classic to 12 volts.

Click here to receive your free copy.

Vintage Car Parts for 12 Volt Conversions - Alternators, Wires, and More

These instructions will work for most 2 wire 12 volt alternators installed in most vintage vehicles, but we also make it easy to get all the parts you need at Vintage Auto Garage. Our 6 volt to 12 volt conversion kits include the alternator, wires with the correct gauge, and plugs, as well as all the other parts you need to complete a voltage conversion.

If you would like a complete list of parts to convert your vehicle to 12 volts, click here and fill out our form and we will send you a complete parts list FREE of charge.

Our team of classic car experts can help you choose the parts for your vehicle. Whether you need assistance to find the right conversion kit for your model year, need advice on which alternator fits best with your vehicle, or have another question, call us at 800-516-4461. Vintage Auto Garage LLC best in class parts for American Classics 

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