Legends - Renegade GPS Speedometer Cluster - Tachometer Connections
(Available on some models)
- 5 -
- negative
+
Yellow wire
1 revolution of engine
8 CYL early style single coil example
(dia 1)
1 revolution of engine
8 CYL twin coil packs
(dia 2)
C2
To spark plugs
Yellow wire
C1
2 revolutions of engine
8 CYL coil on plug
(dia 3)
Yellow wire
Setup the Tachometer to run
2 pulses per rev when
connecting it to the engines’ ECU.
ECU
Tachometer (Yellow)
ACC (12v)
4.7K -10K Ω 0.25 watt minimum
(dia 4)
+
Yellow
wire
Yellow wire
C1
Yellow
wire
Important note: Connecting the tachometer to the wrong wire will NOT damage the tachometer or your ignition.
Note: If you plan to operate the tachometer using OBDII CAN-BUS (J1979), then you do not need to connect the Tachometer signal wire.
FIGURE 9:
Your vehicle ignition system will fall under one of these 4 ignition types. The type of ignition system will determine where the yellow tachometer signal wire
(wire #17) is connected and what the number of pulses per revolution the tachometer should be set to.
Type #1 (single coil) - Up until the 1990’s tachometers picked up the signal from the (-) side on a single ignition coil, reading every pulse sent to all the cylinders.
For example, an 8 cylinder (4 stroke) engine fires 4 spark plugs per revolution or all 8 spark in 2 revolutions. Connecting the yellow wire to the negative side of the
single coil on an 8 cylinder results in picking up 4 sparks in 1 revolution (see diag. 1). This type of ignition was used pre-dominantly until the 1990’s and distributes
sparks to each spark plug. In some vehicles during the 90’s the coil and distributer merged into one unit, but it is the same ignition system - one coil that distributes
sparks to all cylinders. When connecting the yellow wire to this style of ignition you will be picking up all cylinder sparks (see diag. 5).
Type #2 (coil pack) - (diag. 2) is used in the 96 Mustang v8 with twin coil packs. Coil pack #1 (C1) controls the firing of 4 spark plugs and coil pack #2 (C2) controls
the remaining 4 spark plugs. 2 or more separate coils are within each coil pack assembly. In this example each of the 2 coils within each coil pack sends sparks to
2 cylinders at the same time. When one cylinder is firing in the compression stroke, it's paired cylinder is "waste" firing in the exhaust stroke. Each separate coil
within the pack is controlled by it’s own trigger wire. In other words, if you hooked up the yellow wire to one coil trigger wire within one coil pack, it will see only a
fraction of the total engine sparks (see diag. 5).
Type #3 (coil on plug) – An individual coil is placed directly on top of each spark plug eliminating the spark plug wires. The yellow wire , when hooked up to any
coil, will pick up only 1 pulse per 2 revolutions or 1/2 pulse per 1 revolution (see dia 3). For this type of ignition the yellow wire from the tachometer will connect to
the trigger wire on one of the coils. Typically there will be 3 or 4 colored wires coming off of them, but the fourth wire will be blue on one coil and green on the next
coil.
Type #4 (tach output from ECU) Some vehicles will have a tachometer output wire coming from the ECU. The yellow wire from our tachometer can receive signal
Diag 5: Tachometer yellow wire connection
Type #1 ignitions
Type #2- Coil Packs
Type #3- Coil on Plug
Aftermarket ignitions / tach output
- negative
Yellow wire
Yellow wire connects to:
negative side of coil.
12 cyl = 6 Pulses / rev
10 cyl = 5 Pulses / rev
8 cyl = 4 Pulses / rev
6 cyl = 3 Pulses / rev
4 cyl = 2 Pulses / rev
(see Tachometer
Calibration)
Yellow wire connects to:
1 Pulses / rev. (as a good starting point)
(see Tachometer Calibration)
Yellow wire connects to:
1/2 Pulses / rev. (as a good starting point)
(see Tachometer Calibration)
Yellow wire connects to:
tachometer output terminal
12 cyl = 6 Pulses / rev
10 cyl = 5 Pulses / rev
8 cyl = 4 Pulses / rev
6 cyl = 3 Pulses / rev
4 cyl = 2 Pulses / rev
(see Tachometer Calibration)