Chevy 350 Three-Wire Alternator Diagram: BAT, Terminal 1 and Terminal 2
Verified Delco 10SI/12SI three-wire alternator guide for Chevy 350 swaps: BAT output, terminal 1 indicator/excitation, terminal 2 remote sense, grounding.
For a Delco Remy 10SI/12SI/15SI-style three-wire alternator, connect the large BAT output to the battery-positive/common charging junction through cable and circuit protection sized for the alternator and vehicle. Plug terminal 1 is the indicator-lamp/ignition terminal and must receive the application-designed switched excitation circuit. Plug terminal 2 is remote voltage sense and should monitor battery voltage at the battery or a common distribution point. The alternator case must have a low-resistance ground to the engine/battery negative; Delco Remy strongly recommends a dedicated ground lead for optimum performance.
A three-wire alternator is not needlessly complicated. The three conductors perform three different jobs: carry charging current, turn on/control the regulator through the indicator circuit and tell the regulator what voltage the vehicle actually receives. Combining them at the alternator may make a test stand charge, but it sacrifices remote sensing and can create key-off run-on or warning-lamp problems in a vehicle.
Delco Remy's own 10SI/12SI/15SI instructions label these connections directly. BAT is output, 1 is indicator/ignition and 2 is voltage sensing at the battery or common distribution point. That manufacturer definition is the authoritative basis for this page and avoids the common mistake of calling terminal 2 an exciter wire.
Interactive Delco SI three-wire charging map
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This diagram applies only after the alternator is identified as a compatible 10SI/12SI/15SI-style unit. Select each node to trace output, excitation and sensing separately.
Chevy 350 Alternator 3 Wire Diagram
| APPLICATION / ITEM | SPECIFICATION | NOTES |
|---|---|---|
| BAT stud | Charging output to protected B+ junction | High-current cable sized for full output and length |
| Plug terminal 1 | Indicator lamp / ignition excitation | Switched circuit; design must prevent run-on/backfeed |
| Plug terminal 2 | Remote voltage sense | Battery or common distribution point |
| Optional R terminal | Relay/half-system-voltage signal | Not terminal 2 and not battery remote sense |
| Ground | Case + recommended dedicated lead | Engine, body and battery grounds must be sound |
This terminal map belongs to the Delco SI family named above, not every alternator that can be mounted on a Chevy 350. CS130/CS121, one-wire racing units, externally regulated 10DN systems and aftermarket high-output alternators use different connectors or terminal logic. Read the case/part number before wiring.
How to use this specification correctly
- 01
Identify the alternator by Delco series/part number and verify negative-ground, voltage, output rating, pulley and mounting compatibility.
- 02
Disconnect battery negative. Plan the BAT cable from the alternator to a protected battery-positive or common distribution point using output/length-appropriate conductor and protection.
- 03
Wire terminal 1 through the vehicle's designed switched indicator/excitation circuit. Use the alternator/vehicle manufacturer's specified lamp, resistance or isolation method.
- 04
Run terminal 2 to the battery-positive or common distribution point whose voltage should be regulated; protect and route the small sense lead safely.
- 05
Install a dedicated ground lead from the alternator ground boss/case to the engine or primary ground junction, in addition to clean metal mounting contact.
- 06
Route all wiring away from belts, headers and sharp brackets; support the B+ cable so vibration does not load the output stud.
- 07
Reconnect the battery, verify key-on lamp behavior, start the engine and measure voltage at both alternator BAT and the sensed distribution point under load.
BAT output and circuit protection
The BAT stud carries the alternator's full output. The cable must be sized for rated current, length and acceptable voltage drop, and the vehicle requires appropriately located fusible-link or fuse protection designed for charging circuits.
Do not reuse an original low-output ammeter loop or undersized harness wire after installing a higher-output alternator. Bypass or convert legacy ammeters only with a documented circuit design; an unfused high-current wire through the cabin is a fire risk.
Terminal 1: indicator and excitation
Terminal 1 carries full system voltage and connects to an indicator-lamp or ignition terminal according to Delco Remy. In typical vehicles, current through the charge lamp/excitation circuit helps energize the regulator when the key is on and engine stopped.
A direct ignition-feed connection without the designed lamp, resistance or isolation can allow alternator feedback to keep an ignition system energized after the key is switched off. Use the exact regulator/vehicle specification for a resistor or diode rather than copying an arbitrary value or direction.
Terminal 2: remote voltage sense
Terminal 2 monitors battery/system voltage at the battery or common distribution point. When accessories cause voltage drop between the alternator and that point, remote sense lets the regulator adjust output to deliver the intended system voltage where it matters.
A short jumper from terminal 2 to BAT senses only the alternator stud. It may be an approved fallback for some installations, but it cannot compensate for downstream cable/junction drop. Delco Remy recommends taking advantage of remote sensing.
Grounding and belt drive
The alternator's electrical return is as important as B+. Powder-coated brackets, painted heads, corrosion and missing block-to-battery straps can cause voltage difference, noise and unstable regulation. Delco Remy recommends a ground lead for optimum performance.
Belt slip limits output and can mimic an electrical fault. Use correct pulley alignment, wrap and tension; Delco warns against over-tensioning or prying on weak frame areas because bearing and housing damage can follow.
Verification measurements
- Key on/engine off: confirm charge lamp and terminal-1 excitation behavior for the vehicle.
- Engine running: compare alternator BAT voltage with battery/junction voltage.
- Electrical load on: measure positive drop from BAT stud to battery positive.
- Measure negative drop from alternator case to battery negative.
- Confirm terminal 2 sees the intended sensed-point voltage.
- Measure AC ripple to evaluate rectifier/stator condition.
- Switch key off and confirm the engine and alternator shut down without run-on.
Common identification mistakes
- Confusing a 10DN external-regulator plug with an SI internal-regulator unit.
- Calling an optional R relay terminal the remote-sense terminal.
- Using a one-wire instruction for a three-wire regulator.
- Assuming plug cavity numbers from viewing the harness side instead of the alternator face.
- Upgrading output without upgrading B+ protection and grounds.
- Sensing at BAT while expecting compensation for a remote accessory junction.
Chevrolet 350 with Delco 10SI/12SI-style alternator specifications can change by model year, engine, platform, wheel, and installed component. Confirm the VIN or engine identity, part numbers, fastener condition, and the current manufacturer instructions before service.
Chevy 350 Three-Wire Alternator Diagram: BAT, Terminal 1 and Terminal 2 FAQs
What are the three wires on a Chevy alternator?+
On a Delco 10SI/12SI-style setup they are the high-current BAT output, terminal 1 indicator/ignition excitation and terminal 2 remote voltage sense.
Can terminal 2 connect to the BAT stud?+
Some installations permit a local jumper, but remote connection to the intended distribution point provides voltage-drop compensation. Follow the alternator instructions.
Why does my Chevy keep running after I turn off the key?+
Alternator feedback through an incorrectly designed terminal-1 excitation circuit is a common cause. Use the correct lamp/resistance/isolation arrangement.
Is the R terminal the same as terminal 2?+
No. Delco identifies R as an optional relay/half-system-voltage output and terminal 2 as voltage sense.
Does the alternator need a ground wire if it is bolted to the engine?+
Clean mounting contact is part of the path, but Delco Remy strongly recommends a dedicated ground lead for optimum performance.
Technical sources
TorqueSheet favors engine- and component-specific manufacturer instructions over unsourced universal values.
1Delco Remy 10SI/12SI/15SI installation instructionsDelco Remy defines BAT as charging output, terminal 1 as indicator/ignition, terminal 2 as voltage sense and recommends a dedicated ground lead plus application-correct belt and mounting procedures.↗2Delco Remy remote-sense technical guidanceDelco Remy explains that remote sensing measures voltage away from the alternator output stud so the regulator can compensate for distribution-path drop.↗3Delco Remy alternator instruction-sheet libraryDelco Remy publishes model-specific alternator sheets, supporting identification of the exact SI/CS unit before wiring it to a small-block installation.↗