12SI Racing High Output Alternator - One Wire Turn On
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Installation Instructions
Important: A Big 3 wiring upgrade is required for all high output alternators — factory wiring isn't rated for 250A+ output.
Before you start: Batteries fully charged, vehicle off and engine cool. Wear eye protection and remove loose jewelry.
Remove the old unit: Disconnect the negative battery cable, then the alternator wiring. Note the belt routing, remove the belt, then remove the bracket bolts and the factory alternator.
Install the new alternator: Mount it (factory bolts usually work) — hand-thread first, then torque to spec. Fit a serpentine belt about 0.5–1" shorter unless otherwise specified and confirm it's aligned in all pulley grooves.
Grounding: Clean all contact surfaces to bare metal and apply a corrosion inhibitor. On uni-body vehicles, ground to the thickest sub-frame metal and add ground cables if charging voltage is low. Keep wiring at least 12" from heat sources.
Regulator / plug: Factory plug — snap the harness into the regulator. Pigtail (single-wire) — excite wire (L) to a 7–15V ignition source, sense wire (S) to the alternator positive. Self-exciting (one-wire) — no plug; connect only B+ and ground (a battery light may appear). A dash volt gauge is recommended.
Finish: Complete the Big 3 upgrade, reconnect the negative terminal, start the vehicle, and confirm 13.5–14.8V at the battery.
Big 3 Wiring Installation
The Big 3 upgrade replaces the three main cables with 1/0 100% OFC (oxygen-free copper) wire: (1) alternator positive → battery positive, (2) engine/alternator ground → chassis, and (3) battery negative → chassis. Required for all high output alternators.
Before you start: Charge the batteries, vehicle off and cool, eye protection on. Disconnect the negative battery cable first.
Install: Run the upgraded positive cable from the alternator positive to the battery positive. Add an upgraded ground from the engine/alternator bracket to the frame, and another from the battery negative to the frame. Clean every contact point to bare metal and apply a corrosion inhibitor. Crimp and heat-shrink the lugs, then torque firmly.
Finish: Reconnect the negative terminal last. Two kit types are offered — Universal (most common) and Polaris Slingshot (longer positive cable for trunk-mounted batteries). Check the measurements for your vehicle before buying.
Hairpin units are commonly called 6 phase. They produce more output at idle and are more efficient than a conventional alternator. JS Alternators hairpin units feature premium bearings to withstand high engine rpm and utilize dual plate rectifier with 12 heavy duty diodes for improved cooling. Hairpin Units are a more reliable alternator to withstand high heat, high demand for your racing applications
This unit is a direct replacement for standard Delco 10DN, 10SI, and 12SI alternators, making it easy to install on most 1963-1985 GM vehicles. This direct replacement makes for an easy installation! To activate the alternator, you only need to connect a single wire from the provided pigtail to any ignition switched 12V+ source. This allows the alternator to turn on and off with the ignition switch. This unit is for a racing application, be sure to select what pulley design is needed for your vehicle in the drop down menu. Every 250amp alternator will automatically come with the OEM size pulley unless specified in your order notes.
All 12SI Applications will come with a 45 mm. (or 58mm for V Belt) pulley and will require installing a 1/2 inch - 1 inch shorter belt.
Fitment Guide:
| Make | Model | Engine | Year(s) |
|---|---|---|---|
| BUICK | All Early Models | Most Engines | 63-79 |
| BUICK | Gran Sport | All Engines | 65-67 |
| BUICK | Riviera | All Engines | 63-70 |
| BUICK | Skylark | All Engines | 63-79 |
| BUICK | Wildcat | All Engines | 63-70 |
| CADILLAC | All Early Models | All Engines | 63-85 |
| CHEVROLET | All Early Models | Most Engines | 63-85 |
| CHEVROLET | C10 Pickup | All Engines | 63-78 |
| CHEVROLET | Camaro | All Engines | 67-80 |
| CHEVROLET | Caprice | All Engines | 66-77 |
| CHEVROLET | Chevelle | All Engines | 64-73 |
| CHEVROLET | Chevy II | All Engines | 63-68 |
| CHEVROLET | Corvette | All Engines | 63-79 |
| CHEVROLET | El Camino | All Engines | 64-77 |
| CHEVROLET | Impala | All Engines | 63-77 |
| CHEVROLET | Malibu | All Engines | 64-77 |
| CHEVROLET | Monte Carlo | All Engines | 70-77 |
| GMC | All Early Models | All Engines | 63-85 |
| GMC | C15 Pickup | All Engines | 67-78 |
| OLDSMOBILE | All Early Models | V-8 | 63-85 |
| OLDSMOBILE | 442 | All Engines | 65-71 |
| OLDSMOBILE | Cutlass | All Engines | 63-76 |
| OLDSMOBILE | F85 | All Engines | 63-72 |
| PONTIAC | Early models | V-8 | 63-85 |
| PONTIAC | Firebird | All Engines | 67-70 |
| PONTIAC | GTO | All Engines | 64-71 |
| PONTIAC | Tempest | All Engines | 63-70 |
| PONTIAC | Ventura | All Engines | 71-77 |
