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MAC TOOLS EM721 - Page 42

MAC TOOLS EM721
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42
Connect:
Black test probe to the negative (-) battery post.
Red test probe to the point on the fender, re wall, or vehicle frame where the accessory ground is
fastened.
Press the “REC” button (selects the MAX.MIN.AVG function).
Turn on all the accessories (headlights, A/C fan, defroster, windshield wiper, etc.).
Disable the ignition so the engine can’t start and crank the engine for four to ve seconds.
This connection has two connectors, one wire, one ground and one cable terminal-tobattery post; a voltage drop
of more than 0.5V indicates a poor ground circuit.
Clean and inspect the battery cable connections and the ground and test again.
NOTE: Repeat the test after the engine has thoroughly warmed up. Heat expansion may change voltage drop.
Battery Ground to Starter Solenoid (+) Voltage Drop Test
This test checks for battery power efciency to the starter solenoid. Measure the voltage drop between the
battery post and the connecting cable, the solenoid post (+), and the wire that attaches to it.
Red
Black
Solenoid
12V Battery
Starter Motor
Meter setup to check voltage drop:
Set the rotary switch to voltage ( ) setting.
Press the “DC/AC” button until “ ” appears on the display.

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