The Radio Information Board

I have a dual remote head tk-730 G. I have it installed in an ambulance. My problem is that the rear speaker has a hum to it when the ignition is on. The front head speaker is plugged into the remote head, the back speaker is plugged into the control unit, low to 6, high to 12, ground to 15. Control Unit is powered to back side of master switch and unit powers on when master is turned on. No hum is heard when master is on a ignition is off. Any suggestions? Thanks emtposcar

Your post was a little confusing. The speaker connected to the radio deck only uses pins 6 and 12. Not pin 15. If the noise is only present with the key on there may be something in the vehicle causing the noise. Have you tried hooking the rear speaker to the rear head?

first, the reason for the pin 15 is one schematic said that if any accessory was utilized using this plug it needed a ground placed in pin 15. Second, if i plug the speaker directly into the 2nd head the speaker does not work at all. emtposcar

So what is hooked to pin 15?
Also does the noise stop with the ignition off?

Pin 15 is hooked with a wire to a ground bolt on the seat/frame, and yes the hum does quit when the ignition is off. emtposcar

Actually you can disconnect the ground at the seat frame. It's not really doing anything. The radio grounds through the black wire at the main power connector.
Are you connecting the red power lead to the battery?
Can turn off everything and try and isolate what causes the noise?
Double check where the control head cables connect. There is a separate grounding lug that needs to be screwed down to the radio and the head.