Car Radio Muting (Xcrm); Figure 2. Reducer - Nokia NME-2A Series Installation Instructions Manual

P.A.M.S.
Technical Documentation
If the vehicle has +24 V electrical system (trucks, all–terrain vehicles ,
etc.), an external voltage reducer must be used. Since the properties of
the reducer are critical, it is recommended to use a reducer supplied by
the manufacturer. This reducer has good protections against transients
produced by vehicles electrical system and it is also capable of
maintaining stabile output during rapid changes in load current.
Some vehicles have a main switch (e.g. gas trucks), which separates the
vehicles chassis from the negative lead of the battery. Do under no
circumstances pass this switch, i.e. the grounding of the reducer must be
taken from the body of the vehicle, NOT directly from the battery.
WARNING : DO NOT INSTALL REDUCER
– To engine compartment
– Where there isn't adequate amount of air for cooling (under the
carpet, etc.)
– Where there is risk of moisture (condensed water, etc.)

Car Radio Muting (XCRM)

The phone offers a feature that can mute the car radio automatically
during a conversation. This feature is convenient and provides for safer
handsfree operation. The car radio muting feature based on grounded
line, so it means that in standby, the yellow wire (XCRM) is not grounded
and car radio works normally, but during a call, line is grounded and car
radio is muted. The maximum load that this line can handle is 250 mA.
Note that an auxiliary relay or muting unit must be used when the car
radio doesn't have a mute feature available.
Original 08/97

Figure 2. Reducer

NME–2A
Installation Instructions
Page 11