L84sky

Sometimes car engines generate electrical noise. This noise
gets on the 12-volt bus and goes everywhere. Sometimes
you can hear a whine in the radio that changes pitch with
engine RPM. A simple way to reduce or eliminate the noise
is to install a properly sized capacitor between 12 volts and
ground. Capacitors develop an opposition to current flow
called reactance. The amount of reactance a capacitor
produces is dependent on its electrical size (measured
in microfarads) and the frequency of signal applied to it.
The electrical size is fixed at the factory so once it's installed
in the car the only real variable is frequency. There's a
simple formula to calculate the reactance but all that's really
important is that the reactance (measured in ohms) goes
up as the frequency goes down and reactance goes down
as the frequency goes up. The lowest possible frequency
is zero which is the frequency of battery voltage because it
never reverses polarity. Theoretically the capacitor acts like
and open (extremely high resistance) in a DC (direct current)
circuit. My Tracker's noise suppressor filter is installed
electrically between the 20-amp IG fuse and ground G201
through splice pack SP201. Because it acts like an open
it draws no current from the battery. However, if the capacitor
sees an AC (alternating current) signal like the alternator rectifier
ripple voltage, the reactance at that frequency goes down. And
if sized correctly the capacitor will act like a short circuit (very
low or no resistance), but only at that frequency. It still blocks
the DC component. If everything is designed correctly,
noise on the 12-volt power wires is shorted to ground
and disappears.


My Tracker filter capacitor is taped to the outside of the main harness behind the battery.


It's a simple 2-wire connector. The BLK wire goes to ground the BLK/WHT goes to the 20-amp IG fuse.