Overview
The starter and ignition system in 1973-1987 GM Square Body trucks is a critical electrical subsystem that has evolved significantly over this production period. Understanding these systems is essential for Square Body owners, as these trucks commonly experience starter-related issues due to age, corrosion, and the inherent design characteristics of GM's electrical systems from this era.
The starter system consists of the starter motor, solenoid, ignition switch, neutral safety switch (automatic transmissions), clutch safety switch (manual transmissions), and associated wiring. The ignition system underwent major changes during the Square Body production run, transitioning from points-based systems to High Energy Ignition (HEI) and later incorporating computer controls.
Key transition points:
- 1973-1974: Traditional points-based ignition with separate coil
- 1975-1986: HEI (High Energy Ignition) system with integrated coil-in-cap
- 1987: Introduction of Throttle Body Injection (TBI) with computer-controlled ignition timing
Common Issues
Starter System Problems
Hot Start Issues (1973-1987)
- Symptom: Engine cranks fine when cold but fails to start when hot
- Cause: Heat soak causing starter solenoid contacts to expand and create poor connections
- Most affected: Trucks with headers or aftermarket exhaust systems
Starter Solenoid Failure
- Common years: All years, particularly 1980-1987
- Symptoms: Click but no crank, intermittent starting, or complete failure
- Root cause: GM solenoids from this era are prone to contact wear
Ignition Switch Failures
- Peak problem years: 1978-1984
- Symptoms: Intermittent starting, loss of accessories, or complete electrical failure
- Cause: Plastic switch housing degradation and contact corrosion
Ignition System Problems
HEI Module Failures (1975-1987)
- Symptoms: No spark, intermittent running, stalling when hot
- Common failure: Pickup coil and ignition control module
- Heat-related: Modules often fail when engine bay temperatures are high
Distributor Wear (All Years)
- Symptoms: Rough idle, poor performance, timing drift
- Cause: Worn distributor shaft bushings and advance mechanisms
Parts & Materials Needed
Starter System Components
Starter Motors by Engine:
Small Block V8 (305, 350):
- AC Delco 336-1917 (remanufactured)
- Part number varies by year: 1109061 (early), 1109524 (late)
Big Block V8 (396, 402, 454):
- AC Delco 336-1929
- Original GM: 1109072
Inline 6 (250, 292):
- AC Delco 336-1918
- Original GM: 1109056
Starter Solenoids:
Universal Square Body:
- AC Delco D916A
- Standard Motor Products SS-597
- Original GM: 1114350
Ignition Switches:
1973-1977: GM 1990117
1978-1987: GM 26036312
Aftermarket: Standard Motor Products US-95
Ignition System Components
HEI Distributors (1975-1987):
Small Block V8:
- Complete unit: AC Delco D465
- Cap: AC Delco D329A
- Rotor: AC Delco D555
Big Block V8:
- Complete unit: AC Delco D478
- Cap: AC Delco D314A
- Rotor: AC Delco D555
HEI Modules:
Standard module: AC Delco D1906
4-pin module: AC Delco D1977
Available from: Summit Racing, JEGS, local parts stores
Tools Required
Basic Tools:
- Socket set (7mm-19mm, 1/4"-3/4")
- Combination wrenches
- Screwdrivers (Phillips and flathead)
- Wire strippers and crimpers
- Digital multimeter
- Test light
Specialized Tools:
- Starter bench testing equipment
- Timing light (ignition work)
- Distributor wrench set
- Battery load tester
Step-by-Step Guide
Starter Motor Replacement
Preparation:
1. Disconnect negative battery cable
2. Raise vehicle on jack stands or drive onto ramps
3. Safety Warning: Ensure vehicle is properly supported before working underneath
Removal Process:
Step 1: Access and Disconnect
1. Locate starter on passenger side of engine block
2. Remove heat shield (if equipped) - two 10mm bolts
3. Disconnect solenoid wiring:
- Large cable: 13mm nut (battery feed)
- Small wire: Push-on terminal (ignition feed)
4. Support starter weight before removing bolts
Step 2: Remove Starter
Top bolt: 15mm head, 35-40 ft-lbs torque
Bottom bolt: 15mm head, 35-40 ft-lbs torque
Note: Bottom bolt may require universal joint socket
Installation:
1. Position new starter and hand-start bolts
2. Torque bolts to 35-40 ft-lbs in sequence (top first, then bottom)
3. Reconnect solenoid wiring - ensure tight connections
4. Reinstall heat shield
5. Test operation before final assembly
HEI Distributor Service (1975-1987)
Distributor Removal:
1. Remove air cleaner assembly
2. Disconnect distributor cap (4 latches)
3. Mark rotor position relative to distributor housing
4. Mark distributor housing position relative to intake manifold
5. Disconnect vacuum advance line (if equipped)
6. Remove distributor hold-down clamp (12mm bolt)
7. Lift distributor straight up - note oil pump drive engagement
Module Replacement:
1. Remove distributor cap and rotor
2. Disconnect pickup coil leads from module
3. Remove module mounting screws (2 screws, use heat sink compound)
4. Apply thin layer of dielectric grease to new module mounting surface
5. Torque module screws to 25 in-lbs
Ignition Switch Replacement
Column-Mounted Switch (1973-1987):
1. Remove steering wheel (requires puller tool)
2. Remove turn signal switch assembly
3. Place key in "RUN" position
4. Depress lock cylinder retaining tab
5. Remove lock cylinder
6. Remove switch mounting screws (2 screws)
7. Disconnect wire harness connector
Installation Note: Ensure actuator rod is in correct position - switch must be in "RUN" position during installation.
Year/Model Differences
1973-1974 Models
- Ignition: Points-based system with external coil
- Starter: Early solenoid design with different mounting
- Wiring: Single-wire alternator setup
1975-1980 Models
- Major Change: Introduction of HEI system
- Distributor: Large-cap HEI with coil-in-cap design
- Timing: Fixed timing, no computer control
- Starter: Updated solenoid design, improved heat resistance
1981-1986 Models
- Ignition: Refined HEI system
- Computer Integration: Basic ECM integration on some models
- Wiring: Improved harness design and connections
- Reliability: Peak reliability years for starter system
1987 Models
- TBI System: Throttle Body Injection with computer-controlled timing
- EST (Electronic Spark Timing): Distributor timing controlled by ECM
- Wiring: Significantly more complex electrical system
- Diagnosis: Requires scan tools for proper troubleshooting
Model-Specific Considerations
K-Series (4WD) Models:
- Transfer case may interfere with starter access
- Longer starter bolts required in some applications
- Heat shielding more critical due to exhaust routing
Heavy Duty Models (C20, K20):
- Heavy-duty starter motors (higher torque rating)
- Different solenoid part numbers
- Upgraded wiring harnesses
Tips & Best Practices
Starter System Best Practices
Heat Management:
- Always reinstall heat shields - critical for solenoid longevity
- Consider upgrading to modern PMGR (Permanent Magnet Gear Reduction) starters
- Route exhaust away from starter when possible
Electrical Connections:
- Clean all connections with wire brush before assembly
- Apply dielectric grease to prevent corrosion
- Ensure battery cables are properly sized (4 gauge minimum for V8 engines)
Common Mistakes to Avoid:
- Over-torquing starter bolts (causes housing cracks)
- Forgetting to support starter weight during removal
- Mixing up solenoid wire connections
Ignition System Best Practices
HEI System Maintenance:
- Replace cap and rotor every 30,000 miles
- Keep coil terminals clean and tight
- Use only specified spark plugs (AC-44 or equivalent)
Timing Procedures:
- Always disconnect EST connector (1987 models) before setting base timing
- Use quality timing light with advance features
- Set base timing to specification before adjusting advance curves
Module Installation:
- Always use heat sink compound on module mounting surface
- Never touch module terminals with bare hands
- Test pickup coil resistance before installing new module
Troubleshooting
Starter System Diagnosis
No Crank Condition:
Test Sequence:
1. Battery voltage test: 12.4V minimum at rest
2. Ignition switch continuity: Key to "START" position
3. Neutral safety switch: Bypass test for diagnosis
4. Solenoid voltage: 12V at small terminal during crank attempt
5. Solenoid function: Jump large terminals to test motor
Slow Cranking:
Causes and Tests:
- Battery load test: 9.6V minimum under load
- Cable voltage drop: 0.5V maximum drop under load
- Starter draw test: 150-200 amps typical for SBC
- Engine mechanical issues: Compression test if electrical tests pass
Ignition System Diagnosis
No Spark Condition (HEI):
Test Procedure:
1. Check for spark at plug wire: Use insulated spark tester
2. Test pickup coil resistance: 500-1500 ohms typical
3. Check module power: 12V at positive terminal
4. Test coil primary: 0-2 ohms resistance
5. Test coil secondary: 6000-30000 ohms resistance
Intermittent Spark Issues:
Heat-Related Failures:
- Module failure: Test when hot vs. cold
- Pickup coil: Resistance changes with temperature
- Cap and rotor: Carbon tracking when hot
- Coil failure: Secondary breakdown under load
Advanced Diagnostic Techniques
Voltage Drop Testing:
Essential for aging Square Body electrical systems
Acceptable Voltage Drops:
- Battery to starter: 0.5V maximum
- Ground circuit: 0.3V maximum
- Ignition switch: 0.2V maximum
- Solenoid contacts: 0.1V maximum
Load Testing:
Battery: 9.6V minimum at 1/2 cold cranking amp rating
Alternator: 13.5-14.5V at 2000 RPM with electrical load
Starter: Current draw within 10% of specification
Professional Service Recommendations
When to Seek Professional Help:
- Computer-controlled ignition timing issues (1987 models)
- Internal engine timing problems
- Complex wiring harness repairs
- Starter motor rebuilding
Recommended Specialists:
- Electrical shops with classic car experience
- Starter/alternator rebuild shops
- GM dealerships with classic car programs
Parts Sources:
- LMC Truck: Complete starter and ignition components
- Classic Parts of America: OEM-quality reproduction parts
- Summit Racing/JEGS: Performance upgrades and modern alternatives
- Local NAPA/AutoZone: Standard replacement parts with good warranty coverage