How to Diagnose a Car Starter's Command Wire

The starters command wire can be diagnosed very easily. Following these important steps will allow you to find the problem without damaging the vehicles electrical system and without getting shocked.

Difficulty: Moderately Easy

Instructions

Things You'll Need:

• Open end box end wrench
• DVOM
• New starter wire if diagnosed to be inoperative
• Wire brush to remove corrosion
• Safety glasses
• Face shield
• Gloves
• Fender cover

Visual, volt meter, ampmeter, ohm, wire checking steps

1. Disconnect both battery cables from the battery terminals. Make sure they are not resting close to the battery terminals as this could cause the circuit to be closed and possibly give you a shock.

2. The starter command wire runs from the positive terminal on the battery to the positive terminal on the starter solonoid. First, do a visual inspection down the entire length of the wire. Depending on how the wire is run, you may need to use an inspection mirror to see the whole wire down to the starter. Look for cuts, burns, exposed wire insulation and loose connection to the starter solenoid positive terminal. Inspect the positive terminal on the battery for corrosion and the positive terminal on the starter solenoid.

3. Using digital volt ohm meter, set the meter to the ohms position and place the positive lead from the meter onto the eyelet at the battery and the negative wire to a metal ground source. The reading should read 0 or very close to 0. If a high ohms reading exists, the wire is damaged under the insulation and should be replaced. Use the same technique to probe every few inches of the wire checking for any high ohms readings.

4. Connect both battery leads to the positive and negative terminals. Reconnect the other end of the wire to the positive terminal on the starter solenoid. Using the volt setting on the meter, touch the positive lead to the eyelet at the starter solenoid and the negative lead to a metal grounding surface. Crank the engine for 5-10 seconds. If voltage is less than 12-14 volts, either the battery is low or there is a short somewhere in the wire. Wire should be replaced.

5. Set meter to amps and place one lead at the positive lead going to the starter. Place the negative lead to a ground surface. Crank the engine for 5-10 seconds and note the amp reading. The reading should be between 140-200 amps. Voltage should be the same as the battery voltage during cranking. If readings are lower than normal, the wire should be replaced.

Tips & Warnings

• Safety glasses should be worn throughout the procedure and face shield if battery appears bulged.
• If battery is bulged do not proceed with steps to check the starter wire. Put on a face shield, gloves and safety glasses and gently remove the battery. Bulging indicates shorting inside the battery and could cause injury if dropped or cracked.