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4. Check for a microphone line (white/black, white/orange, white/
brown, orange, or tan wires) shorted to the headphone line (blue
wire). The short could be at one of the headset jacks or in the
wiring between the unit and a jack.
Note that for 2 and 3 above, it will only squeal if a headset is
actually plugged into the specific jack that is wired incorrectly.
PTT Test:
If all above is good, make sure all headsets are plugged into their
respective jacks. Put on the Driver’s headset and position the micro-
phone as usual. Press the Driver’s PTT switch. While continuing to
hold down the switch, talk into the mic and verify that you can still
hear yourself. Also, while holding down the PTT switch, verify that
none of the other headset microphones are active. Release the
PTT switch.
Now put on the Passenger’s headset, position the microphone, and
press the Passenger’s PTT switch. Verify that only the Passenger’s
headset microphone is active as his switch is held down.
If the system has a jack and PTT wired up at the vehicles Driver’s
Auxiliary panel, unplug the headset from the Drivers position and
plug it into the Driver’s Auxiliary jack. Press and hold down the
Driver’s Auxiliary PTT switch. Verify that only the Driver’s Auxiliary
headset microphone is active.
If all works fine, skip down to “Electrical Noise Test” section. If
anything does not work as above, you have one of three possible
PTT switch wiring errors:
1. PTT line (white/red, white/blue, white/green, or yellow wires)
open or not connected between a PTT switch and the UltraSound
unit.
2. Open or missing return line (black wire) to a PTT switch.
3. Reversed PTT lines. The Drivers PTT line connected to the Pas-
senger’s PTT switch and vise versa.
Electrical Noise Test:
The last thing to do before the radios are hooked up to the unit is a
simple noise test to verify system wiring as well as vehicle electrical
system integrity.
1. Unplug all intercom headsets except for the Drivers.
2. Make sure all the UltraSound panel controls and switches are set
as in “System Setup” section.
3. Start the vehicles engine and let it idle a bit. This is a stationary
test — the vehicle should not be moving and should be in “PARK”
or “NEUTRAL” with brakes set.
4. Close all vehicle windows and doors to eliminate as much back-
ground noise as possible.
5. Turn on as much vehicle electrical equipment as possible. This
usually means all lights and strobes. Do not turn on sirens or horns.
6. Put on the Driver’s headset, position the mic, and make sure the
headset volume control is set to maximum.
7. With the vehicle still in “PARK” or “NEUTRAL” and brakes set, slowly
increase the vehicle engine rpm from idle to about 1500 RPM and
back again. While doing this, listen for any whine or hum in the
headsets. Except for some possible engine background noise
being picked up from the headset microphone you should not
hear any “Electrical” whine or hum in the headset.
8. Shut off the vehicle engine as well as the lights, strobes, etc. If,
while the engine was running, there was no electrical noise, skip
down to “Radio Hook Up” section. If you did hear electrical noise,
use the following to track down the problem:
Turn the vehicle power off and disconnect the UltraSound ground
connection (green wire) from ground. Turn on the vehicle power
(engine off), put on the Driver’s headset and see if the intercom
part of the UltraSound unit is working.
IF YOU CAN HEAR YOURSELF IN THE HEADSET:
1. Then the UltraSound intercom return wire (black) is incorrectly
grounded to the vehicle chassis. Look for:
a) A headset jack barrel touching the vehicle chassis. Most
common when a headset jack is mounted directly into the
vehicle’s panel without using the supplied insulating washers
or incorrectly installing the washers.
b) The black wire pinched or cut and shorting to the vehicle
chassis. This can be anywhere along the intercom wiring as
the black wire goes to all headset jacks and PTT switches.
2. Once the problem has been found and fixed, again make sure
that the intercom now does not work with the green wire dis-
connected. You could have the black wire grounded in more
than one spot.
3. The next step is to reconnect the green wire and do the electrical
noise test again to assure that you have fixed all possible noise
problems.
IF YOU CANNOT HEAR YOURSELF IN THE HEADSET:
The intercom wiring is correct, but excessive electrical noise from
the vehicle’s power system is affecting the UltraSound unit oper-
ation. This noise is getting into the unit on the UltraSound power
wires (red and green). There are basically two types of power line
electrical noise sources:
1. Noise generated directly by the vehicle’s electrical/ charging
system — most commonly known as alternator whine. This is
only present when the vehicle’s engine is running and recognized
by the fact that the pitch or frequency of the whine changes
directly with the change in engine rpm. (Higher frequency at
higher engine rpm’s and lower frequency at lower rpm’s.)
The preferred way to solve this type of problem is to have the
vehicle’s electrical / charging system serviced. The most common
cause of this type of noise is bad diodes in the vehicle’s alternator.
Other possible causes are: Bad vehicle voltage regulator; Bad
alternator or battery cable connections; Missing or bad engine
or alternator grounding straps.
If servicing the vehicle’s charging system is impractical, installing
a good alternator whine power line filter between the vehicle
power and the UltraSound red wire will usually accomplish the