1. Using the DMM

3. Watt is being measured?
Volts
Amps
Ohms
Watts
Weight

6. Resistance Tests Tests a circuit or component statically
Does not confirm if something is “good”
Can confirm if something is “bad”
Useless for finding certain problems
Good for finding other problems

7. Ohm reading?
1 ohm
2 ohms
.5 ohms
No ohms OL
OMG?

8. Bulb resistances: Typically low Typically high Typically OL
Typically OMG

9. Or the component is disconnected from the vehicle

12. Why does an open switch read OL?
Low resistance
High resistance
Infinite resistance
Confused DMM
b/c its LOL without the L

13. A closed switch should read?
0.0 ohms
Less than 1 ohm
More than 1 ohm OL
High resistance

14. Why a resistance test isn’t perfect
How many ohms does this wire have?
Is it OL?
Low Resistance?
How much current will it carry?

17. This may cause? A blown fuse No light operation Dim light operation
Nothing
1 and 3
2 and 4
2 – 4
2 – 3

18. Unwanted Resistance Generally in the form of corrosion
Can be green but may not appear at all
Broken wire strands = increased resistance
Fretting and thermal cycling
May not show up during resistance measurement

19. Voltage Drop Testing
Tests the circuit dynamically – this means the circuit must be in operation!!!!
Shows how much voltage is getting to a spot
Shows how much voltage is being used
Shows how much voltage is left
Much better than a resistance test

20. Voltage drop means? Voltage available to a load Voltage used by a load
Voltage not used by a load
Ooops, I dropped the DMM when I was measuring voltage

21. Why are the drops 12 volts? Because they’re parallel
Because each gets battery voltage
Because each has ground
Because each is the only load

25. Did the last slide show voltage drop testing?
Yes No
Not sure

26. Not voltage drops
The DMMs are placed to measure voltage at a point in the circuit

28. Testing voltage
To test for voltage (available voltage or source voltage) – negative lead on ground somewhere
Positive lead placed at test location – usually the power supply to a load
Indicates the voltage difference between the two leads only

29. Checking fuses = checking for voltage

30. Circuits 101 Complete path for electron flow
Positive side and negative side
Contains
Power (positive)
Ground (negative)
Circuit protection
Control
Load
Conductors