© 2004 directed electronics, inc.
19
IIM
MPPO
ORRTTA
AN
NTT!! Do not use any testing tool other than a digital multi-meter to prevent
costly damage to the vehicle. Use of a test light may cause grounding of sensitive elec-
trical components that can damage the on-board vehicle computer and processors
resulting in substantial cost for replacement.
How to find a tachometer wire with your multimeter:
1.
Set to ACV or AC voltage (12V or 20V is fine).
2.
Attach the (-) probe of the meter to chassis ground.
3.
Start and run the vehicle.
4.
Probe the wire you suspect of being the tachometer wire with the red probe of
the meter.
5.
If this is the correct wire the meter will read between 1V and 6V and fluctuate
with the RPM of the motor.
finding the wait-to-start bulb wire for diesels
In diesel vehicles it is necessary to interface with the wire that turns on the WAIT TO
START light in the dashboard. This wire illuminates the bulb until the vehicle’s glow
plugs are properly heated. When the light goes out the vehicle can be started. This
wire is always available at the connector leading to the bulb in the dashboard. It can
also be found at the Engine Control Module (ECM) in many vehicles.
To test and determine the polarity of this wire:
1.
Set your multimeter to DCV or DC voltage (12 or 20V is fine).
2.
Attach the (+) probe of the meter to (+)12V.
3.
Probe the wire that you suspect leads to the bulb with the (-) probe of the meter.
4.
Turn the ignition switch to the ON position.
5.
If the meter indicates 12 volts until the light goes out you have isolated the cor-
rect wire and the wire's polarity is negative (ground while the bulb is on).
6.
If the meter reads zero volts until the light goes out and then reads 12 volts, you
have isolated the correct wire and the wire's polarity is positive.
warning!
On vehicles with air bags or supplemental
restraint systems (SRS) you may notice a bright yellow
tube with small wires in it marked SRS underneath the
steering column near the key cylinder. DO NOT tamp-
er or unplug these for any reason to prevent costly dam-
ages to your vehicle or personal injury. Tampering may
cause unintended deployment of airbags, resulting in
injury.
