This alternator is a Delco 20SI-style unit built for Caterpillar industrial and marine equipment applications, engineered to OEM specifications for a direct, bolt-in fit and function replacement. The same Delco 20SI footprint is also used across a range of Chevrolet/GMC medium-heavy duty trucks, Cummins industrial engines and International trucks, so this unit cross-references to those applications too.
It is internally regulated (IR), which means the voltage regulator is built into the alternator housing rather than fitted as a separate external component, simplifying wiring and reducing points of failure. It also has negative ground polarity, bi-directional rotation, and carries a threaded R terminal for straightforward OE-style wiring. Output is 12 volts at 60 amps, matching the original Delco 20SI specification this unit is built to.
Key Features
- Delco 20SI-style design for direct OEM fit and function
- 12 volt, 60 amp output
- Internally regulated (IR), negative ground
- Bi-directional rotation
- Threaded R terminal for OE-style wiring
- Also cross-references to Chevrolet/GMC, Cummins & International applications
Technical Specs
| Specification |
Detail |
| Alternator Family |
Delco 20SI |
| Voltage |
12V |
| Amperage |
60A |
| Rotation |
Bi-Directional |
| Regulator Type |
Internal (IR) |
| B+ Terminal |
1/4-28 Threaded |
| Ground Polarity |
Negative |
Years shown are the overall coverage span for this part. Please confirm against the OEM part number on your original unit before ordering.
Vehicle Fitment Guide
| Make & Model |
Years |
| Caterpillar Marine Engines (3208, 3306, 3406, 3408, 3412) |
Not specified by manufacturer |
| Chevrolet/GMC C-Series, Kodiak & Topkick Medium-Heavy Duty Trucks |
1989-1993 |
| Cummins Industrial Engines (B, C, K, L, V Series) |
1980-1985 |
| International Trucks |
Not specified by manufacturer |
OEM Part Number Cross Reference
Aftermarket replacement. OEM part numbers are listed for reference only.
| Part Number |
Manufacturer / Brand |
| 321-666 |
AC Delco |
| ADR0010 |
Arrowhead |
| 7G7889 |
Caterpillar |
| 1117621, 1117624 |
Delco |
| 3016628 |
Cummins |
| 586986C91 |
International Harvester |
| 7266, 7651 |
Lester |
Frequently Asked Questions
Will this fit without modification?
Yes, this alternator is built to the Delco 20SI specification for a direct, bolt-in fit on compatible Caterpillar, Chevrolet/GMC, Cummins and International equipment - no modification is required.
What's included?
You receive one fully assembled 12V 60A alternator, ready to install.
How do I know my old alternator has failed?
Common signs include a dashboard charge warning light, dimming or flickering lights, a battery that will not hold charge, or unusual whining noises from the unit.
Is the regulator built in?
Yes, this is an internally regulated (IR) unit, so no separate external regulator is required.
Dispatched from the UK · 12-month warranty · Fitment support from our technical team
