Installation Guide

Draft
Chapter 4 Best Practices: Installation & Troubleshooting
In this section are Motorola recommended vehicle installation practices that can address or prevent
many issues, including:
• Radio circuit damage due to over voltage condition
• Radio/Accessories "lock up"
• Radio/Accessories change state/lock-up when radio PTT is depressed
• Radio intermittently resets
• Alternator whine present when transmitting with engine running
• Radio/Accessories turn themselves on/off
4.1 Check Wiring of Ignition and Radio Ignition Sensing
• If it is required to turn the radio on and off via the ignition sense switch, in addition to the control
head’s on/off switch, connect the ignition sense lead to the accessory terminal from the ignition
switch (usually in the vehicle’s fuse panel under accessory or radio).
NOTE: Motorola recommends protecting or isolating the radio’s ignition sense input from voltage spikes
in excess of +/- 40 VDC. Such spikes can be hundreds of volts in amplitude and are common in
larger vehicles (utility trucks, buses and etc.), especially when the source is common to a
solenoid coil. A triggerable oscilloscope is required to determine the existence of such spikes as
most voltmeters cannot measure in short duration (< 1 msec). If the condition of the intended
ignition sense source is unknown, Motorola recommends isolating the source from the radio with
a relay or the use of a suppression diode wired between the source and ground. Any high current
suppression diode (i.e. MR2535) with a breakdown voltage of between 18 and 40 volts will
suffice. A suitable diode kit is available from Motorola parts, kit number HLN6325_.
• If it is required to have the radio power up only via the control head’s on/off switch, then connect
the ignition sense lead directly to the positive terminal of the battery. This will mean the ignition
sense will always be ignored and a re-wiring will be necessary in the future if the operator
chooses any ignition sense CPS setting.