12V Marelli Style Alternator for Caterpillar 420D, 422E, 432E, 442E, D4H XL, TH414C 1998-2023

This one is 12V. It is rated at 120 amps. Voltage has to match your machine exactly. A 12V unit on a 24V system will be damaged, and a 24V unit on a 12V system will crank slowly or not at all. If you are unsure, check the battery setup: two 12V batteries wired in series usually means a 24V system.

This unit turns clockwise. Rotation is read looking at the drive end, the end the pulley or gear sits on. Most alternators driven by a serpentine belt turn clockwise, but always match what came off.

We list 116 vehicle and equipment applications for this alternator. Use the "Does it fit?" checker further up this page to pick your make, model and year, or open the full applications list.

The surest check is the number stamped on the unit you are replacing. Match it against the cross reference numbers on this page. Fitment lists are a guide, and the same machine can leave the factory with more than one setup, so the number on your old part beats a model year every time.

Probably yes. One unit is sold under many numbers by the vehicle maker, the original manufacturer and the aftermarket. The cross reference list on this page shows the numbers we know map to this alternator. If yours appears there, this is the right part.

If your number is not listed, try our cross reference lookup. It searches every number we hold, not just the ones shown here.

12739 is the Lester number. Lester is the long standing industry catalogue for rotating electrical, and its numbers are how the trade identifies a unit regardless of who sold it. We use it as our part number because it is the one identifier that stays stable across every brand that has ever boxed this alternator.

With the engine off, a healthy battery reads about 12.6 volts. Start the engine and read again: you should see roughly 13.8 to 14.4 volts at the battery. If it stays at battery voltage or drops, the alternator is not charging. If it climbs above about 15 volts, the regulator is overcharging, which boils batteries.

A warning light that glows dim, headlights that fade at idle, or a battery that keeps going flat overnight all point the same way. Have the battery load tested first, since a failing battery can drag a good alternator down and look identical.

Start with what the machine came with and go up only if you have added load. Light bars, winches, inverters, extra beacons and audio all draw continuously. Sizing up is usually safe, since an alternator only delivers the current the system asks for, but the belt and the charging cable have to carry it.

Going below the original rating is the mistake to avoid. It runs the unit at full output constantly and shortens its life.

IR means internally regulated, so the voltage regulator lives inside the alternator. EF and IF describe whether the field is external or internal. A self exciting alternator starts charging from engine speed alone and needs no ignition wire to wake it up.

These decide the wiring, so they are not cosmetic. The glossary spells out every code we use, and each one links to the parts that carry it.

New. Every alternator we list is a new unit, not a rebuilt core, and it carries a one year warranty. There is no core to return and no deposit to chase.

Orders leave within three business days. Ships from USA. You can read the full terms in our shipping policy, and returns are covered in the return and refund policy.

Returns are accepted within the window set out in our return and refund policy,and a restocking fee applies unless the part is defective or we made the error. A unit that has been installed or used cannot be returned, so it is worth confirming fitment by part number before you fit it.