Engine electrical work

Five procedures. Wiring technique is in AF-K Procedures and is not repeated here.

Procedure 0 — De-energize, in an engine bay (R2, R3)

1. Master off, and disconnect the battery where the work touches starter or charging circuits. Those circuits carry hundreds of amps.
2. Magnetos grounded (PP-H Procedure 0) — you are working near a propeller.
3. Confirm dead at the point of work.
4. Remove rings and watches, and use insulated tools.

Check — point at the disconnected battery lead. A master switch is not isolation for a starter circuit.

Procedure 1 — Inspect engine electrical wiring (S1, S8, S15, R4)

1. Separation from fluid lines — and note anything routed below a fluid line (PP-F Concepts §1).
2. Clamping: interval, condition, correct type, not over-tightened.
3. Chafe: at clamps, at structure, at anything that moves. Note which way the chafe runs.
4. Heat damage: hardened, cracked or discolored insulation, especially near exhaust.
5. Fire sleeve present where required, and in good condition.
6. Connectors: security, sealing, backshell condition, corrosion.
7. Terminals: security, corrosion, correct type, and no more than the permitted number per stud.

Check — look above every wire run for a fluid line. That is the engine-bay specific inspection and it is the one that prevents fires.

Procedure 2 — Determine wire size for an engine circuit (S9, K8)

1. Establish load current and duty.
2. Establish run length, out and back.
3. Select on current capacity and voltage drop, taking the larger (AF-K Procedures Procedure 1).
4. Apply the temperature derating for engine-compartment ambient — this is the step that differs (PP-F Concepts §2).
5. Apply bundle derating.
6. Size the protective device to protect the wire, also derated.

Check — state the ambient temperature you sized for. A size chosen without it is a cabin size in a cowling.

Procedure 3 — Replace a generator or alternator (S3, S4)

1. Procedure 0.
2. Note belt or drive arrangement, mounting and any shims.
3. Disconnect electrically, labeling and capping.
4. Remove, supporting the unit.
5. Confirm the replacement part number is eligible for this engine and installation (S2, GEN-I Procedures Procedure 5).
6. Install, torque per the manual, set belt tension where applicable to the specified figure.
7. Reconnect, confirming polarity (PP-F Concepts §3).
8. Functional check: output voltage at the specified RPM, and regulator function.

Check — confirm polarity before energizing, and state it aloud. This is the one failure in this curriculum that is immediate and expensive.

Procedure 4 — Troubleshoot a charging system (S5, S12)

1. Predict: what should the system voltage be at what RPM (GEN-A Concepts §2)?
2. Measure system voltage at the bus, engine running, at the specified RPM.
3. If there is no output, check the field circuit first — breaker, switch, regulator supply, field wire. An alternator without field excitation produces nothing and is not faulty (PP-F Concepts §4).
4. Check the ground — both the unit's ground and the engine bonding (S13).
5. Voltage drop along the output cable under load (GEN-A Procedures Procedure 5).
6. Then consider the unit itself.
7. Use the wiring schematic throughout (S12).

Check — say which of field, ground, cabling and unit you have eliminated. Replacing an alternator that had no field supply is the classic wasted repair here.

Procedure 5 — Remove and install a starter (S6, S7)

1. Procedure 0 — battery disconnected.
2. Note the drive arrangement and orientation.
3. Disconnect the heavy cable, insulating the end, and any control leads.
4. Remove, supporting the unit — starters are heavy.
5. Install with correct hardware, confirm the drive engages correctly, torque per the manual.
6. Reconnect, heavy cable last, correct polarity.
7. Functional check, and check for correct disengagement after start.

Check — confirm the drive disengages. A starter that stays engaged after the engine fires is destroyed within seconds, and it takes the ring gear with it.

The checks, collected

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