250V MAX
15A MAX
FUSED
COM
DC
15A
20M
200
K
20K
2K
200
8CYL
6CYL
TACH
X10
5CYL
4CYL
8CYL
OHMS
15
A
11
To measure Engine RPM (TACH) (see Fig.
12):
1. Insert BLACK test lead into COM test
lead jack.
2. Insert RED test lead into
test
lead jack.
3. Connect RED test lead to TACH signal
wire.
• If vehicle is DIS (Distributorless Ignition
System), then connect RED test lead to
the TACH signal wire going from the DIS
module to the vehicle engine computer.
(refer to vehicle service manual for loca-
tion of this wire)
• For all vehicles with distributors, connect
RED test lead to negative side of primary
ignition coil. (refer to vehicle service
manual for location of ignition coil)
4. Connect BLACK test lead to a good
vehicle ground.
5. Turn multimeter rotary switch to cor-
rect CYLINDER selection.
6. Measure engine RPM (TACH) while en-
gine is cranking or running.
7. View reading on display.
• If using LO TACH, display reading is
actual RPM.
• Remember to multiply display reading by
10 to get actual RPM.
If display reads 200, then actual engine
RPM is 10 times 200 or 2000 RPM.
7. Switch RED and BLACK test leads and
repeat Step 6.
8. Test Results
If the display showed:
• A voltage drop of 0 volts in both direc-
tions with the continuity beeper sound-
ing off, then the diode is shorted and
needs to be replaced.
• A “1” appears in both directions, then the
diode is an open circuit and needs to be
replaced.
• The diode is good if the display reads
around 0.5V–0.7V in one direction and a
“1” appears in the other direction indicat-
ing the multimeter is overranged.
Measuring Engine RPM
(TACH)
RPM refers to revolutions per minute. When
using TACH you must multiply the display
reading by 10 to get actual RPM. If display
reads 200 and the multimeter is set to 6
cylinder TACH, the actual engine RPM is 10
times 200 or 2000 RPM.
Typical
Ignition
Coil
Ground
Black
Red
Fig. 12
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