Jamar RAC Plus I, User Manual

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RAC Plus I User’s Manual
2-8
is switched off with the ignition key.
We also recommend the circuit should
have as few devices as possible to avoid
voltage fluctuations from Turn Signals,
Brake Lights, etc. Plug the power cable
into the hole labeled
Power
on the
MDS, as shown in Figure 2.6.
Adjusting the Vehicle Speed Sensor Pulse Rate
The signal pulses coming from the vehicle speed sensor are generated for
use by the vehicle’s computer, engine/transmission control, fuel manage-
ment, ABS brakes, etc. The pulse rate can vary from 4,000 to in excess of
100,000 pulses per mile. The MDS will condition and amplify these pulses
for use by the DMI. Since the higher
pulse rates are not required for accu-
rate distance measurements, the MDS
incorporates a divider circuit to reduce
the pulse rate. This is done by adjusting
the
rotary switch
on the front of the
MDS, as shown in Figure 2.7.
The adjustments go from 1 to 1 (1 pulse
into the sensor, 1 pulse out) through
64 to 1 (64 pulses into the sensor, 1 pulse out). Although your particular
vehicle may vary, generally Chrysler and Ford vehicles use a 4 to 1 ratio
(position 4 on the switch) while General Motors vehicles use a 16 to 1 ratio
(position 16 on the switch).
To adjust the ratio, use a small screwdriver to turn the switch to align it
with the number you want. Note that the switch is at the '1' position when
switch is turned fully counterclockwise. It is at the ‘Test’ position when the
switch is turned fully clockwise.
The Tap Test positions are explained in the troubleshooting section on page
3-4. You may need to adjust the ratio again based on the results of the cali-
bration procedure described in Chapter 3. Any time you change the pulse
ratio, you will need to re-calibrate the DMI.
Once you have installed the MDS, install your RAC Plus using the instruc-
tions on page 2-15.
Fig. 2.6 –Power Plug-in
Fig. 2.7
Rotary Switch Adjustment