Ford — Starter Motor - Motor Ground Circuit (Voltage Drop Test)

Testing & diagnosis · Starter motor ground circuit

From a Ford service manual — check it applies to your exact model before use.

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Procedure

1. Disconnect the inertia fuel shutoff switch (on road vehicle only).
2. Connect a remote starter switch between the starter motor solenoid S-terminal and the battery positive (+) terminal.
3. Connect the 73 Digital Multimeter positive lead to the starter motor housing (clean and free of rust or grease). Connect the negative lead to the negative (-) battery terminal.
4. Engage the remote starter switch and crank the engine. Read and record the voltage reading. The reading should be 0.5 volts or less.
5. If the voltage drop is more than 0.5 volts, clean the negative cable connections at the battery and body connections, and retest.
6. If still greater than 0.5 volts, determine which way the current is flowing in the cable and check each end with the multimeter.
7. If the voltage drop is too high, clean the terminal ends. Retest, and if still high, replace the cable. If the reading is less than 0.5 volts and the engine still cranks slowly, replace the starter mo

Source: Ford service manual. Steps and values are as documented; always cross-check against the official manual and any later revisions for your exact serial number before servicing.

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