SOLVING AM RADIO INTERFERENCE PROBLEMS

I like to listen to the AM talk shows while we travel in our D.  Although reception on the AM band with most car radios today leaves something to be desired, the electrical noise on the radio severely limited my enjoyment of the AM radio.  Most of the noise comes from the cooling fan for the air conditioner radiator that is mounted longitudinally between the front wheels.  DC motors are notorious for generating radio-frequency noise, and this one seems especially bad.

However, this problem is (relatively) easily solved.  You will need to purchase and install a power noise filter, which you can get at either WalMart or Radio Shack.  The factory AM/FM radio is protected by a 10 amp fuse, so I selected a Scosche model ES-004 noise filter rated at 10 amps.  Cost at WalMart was less than $9.  If you need to filter more than 10 amps, you will need to get an appropriately-rated noise filter (probably from Radio Shack).

Installation of the noise filter is straightforward.  For best results, the noise filter should be installed in the power lead close to the radio.  For access to the rear of the radio on my 98 36T, I first removed the six screws securing the plastic wood dash to the dash cover.  Then I removed the dash cover, which is the "domed" plastic unit by removing the screws in back of this cover and also on the bottom below the little cubbyhole.  Once these screws are removed, you can remove this plastic dome entirely.

Now, for access to the rear of the radio, you must remove the rearview monitor.  Remove the four screwknobs that secure it to its platform, and CAREFULLY pull forward on the plastic wood dash whilel pulling back and up on the monitor.  Once the monitor is removed, you have access to the wiring harness on the rear of the radio.  On my radio, I had to connect the noise filter in series with the pink wire, which is the unswitched 12 volt DC input to the radio.  The noise filter ground lead is easily connected to the mounting bar of the monitor by using one of the screws that mounts the monitor bracket to the mounting bar.
I soldered my electrical splices and wrapped with electrical tape, although you could also use wire nuts.  DO NOT just use electrical tape to hold the wires together.

Total time for this project was about 45 minutes, and now I can enjoy the AM radio with the bus air turned on.

Note - You should first check to make sure that your antenna is grounded to the frame at the base of the mast. Also, if this does not solve your problem, you may need to add some capacitors across the battery feed at the fan motor.

-Submitted by Bob Cook