You can install both a 'capacitor' style
filter, but be sure and install one on both
the +12BATT & the +12V-ignition....one or
both of these could be a source of noise.
Also beware that you may need to also install
a 'choke' basically a transformer thing..
a coil of wire wrapped around a magnet of
sorts "an inductor" Just make sure if you
install this, to get one rated for the amount
of current you device draws (amps). Moving
the ground can also help...as well as making
sure your antennna lead is not routed next to
say the fan motor and that it too has a good
ground at the fender mount.
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71 Chevy C-10 SWB Fleetside WAS:307w/3-on-the-tree NOW:350TBI/700R4/3.73
See it at
www.prismnet.com/~grzanich