Thread: Feedback from siren speakers: Siren off. Truck off. Master off. Shoreline plugged in

We have a 1995 Frontline (E-One) Ambulance used as our rescue vehicle. Over the last few months, there has been problems with the truck being dead if not plugged in over a couple of days. I rarely respond in the vehicle so I don't know much about it. I noticed today, an electrical humming noise (sounds identical to the auto charge) coming from both siren speakers. They're mounted under the front bumper. Unplugged the shoreline and the noise stops.

The siren is a whelen and is in the OFF position. (It is mounted in a console in the front of the cab)
Both master power switches are in the OFF position.
The ignition is in the off position.
Shoreline power is plugged into the auto eject with Auto charge. (mounted in the drivers side compartment and plugged in just above)

Everything on the truck is just the way it came from the factory. No hacking has been done on the wiring of the truck. I've confirmed this.

Any ideas where I could start looking for a short, or a "leak" of power, or what might be going on?
Thanks
Craig

sounds like you could be picking up RF noise from the AC shoreline.

Im thinking maybe the master switch needs to be checked/replaced. Even though its off, it may need to be allowing just enough juice through to cause the feedback. Any thoughts on that?
Craig

Disconnect the wires on the back of the shoreline socket and check resistance between the two load-carrying contacts. Sometimes road grime or salt can cause current leakage between the contacts and that leakage can cause clicks and hums in the siren speaker.

Just wait it out, the short in the back of the shoreline will eventually arc and catch on fire, resulting in the purchase of a brand new rig! LOLOL, problem solved!

No seriously, as previously stated, check the shoreline connections. The noise from the shoreline may actually be transmitting through other wires or the chassis itself causing the speakers to hum. They are magnets afterall.

Refresh my memory, on checking contacts. I've only recently learned how to use a multimeter. I know how to check voltage, continuity, but im not sure on the resistance.
What should I see on the display etc?
Thanks
Craig