Initial Inspection

We began with a charging system inspection. At first, the car was charging at 14 volts while cold, which is normal. However, after running for 10 to 15 minutes, the voltage dropped steadily, eventually leveling out around 13.4 volts. A quick wiring check revealed a critical issue: the positive cable was too hot to touch, a clear indication of trouble. Cables should generally stay at room temperature under normal operation.

Voltage Drop Testing

Using a digital volt-ohm meter (DVOM), we performed a voltage drop test to pinpoint the issue. Here’s how we set it up:

1. Connection Points:
   • The negative lead of the DVOM was connected to the starter.
   • The positive lead was connected to the positive battery post.
2. Expected Results:
   • A voltage drop of no more than 0.25 volts is acceptable.
   • Ideal readings should be closer to 0.01 or 0.07 volts.
3. Actual Findings:
   • The reading showed a staggering 0.7 volts—far above the acceptable range, confirming excessive resistance in the cable.

Thermal Imaging and Cable Analysis

Using a thermal imaging camera, we investigated further:

• The positive cable showed a temperature of 135–150°F, far too high for safe operation.
• Although there were no visible signs of severe corrosion, internal oxidation of the copper wires likely caused the resistance and overheating.

To confirm, we pierced the cable insulation a few inches back and found a voltage difference between the connection points—further evidence that the cable’s integrity was compromised.

Solution: Replacing the Cable Assembly

We replaced the positive cable assembly, which also included a new negative cable. Once installed, we performed thorough testing:

• The car now charged consistently at 14 volts, even after 20 minutes of driving.
• The previously overheating positive cable remained cool to the touch.
• Both the radiator fan and interior blower motor operated flawlessly.

Final Verification

We tested the car under various conditions:

• With the blower motor running at full speed, then reducing to lower speeds.
• After driving and idling with the radiator fan cycling.

The system held steady at 14 volts. The blower motor, which previously turned off randomly, worked without a hitch throughout the test.

Conclusion

The issue stemmed from internal oxidation and poor connections within the positive cable, not the alternator—a common misdiagnosis in such cases. The new cable assembly resolved all issues. No more jump-starting or blower motor glitches!

Outcome: One happy customer and a fully functional Porsche 944.

If you’re troubleshooting a similar issue, always test cables thoroughly and don’t rush to replace components like the alternator without verifying the true root cause.