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Author Topic: One, Two, or Three Wires?  (Read 2104 times)

Posts: 27


« on: January 10, 2001, 10:50:48 AM »

I am attempting to install a mobile radio (706MKIIG). Is it necessary to run one wire from each battery terminal to the radio? With a separation kit,        the radio will be in the trunk. Car audio install-people that install huge amplifiers into the same location, use one wire from the positive battery terminal, and run the negative side directly to the     car chassis (Ground - 18" or less away from the device). They sight the fact that the negative terminal of the battery is attached to the chassis in the engine compartment and state that the second wire run from the battery is redundant and unnecessary. Also, they are quick to point out that connecting to the chassis will reduce the noise interference.

Would I be able to install a mobile radio where the red) wire is attached to the battery, the (black) wire is attached to the chassis (18" inches away from the radio), and the ground wire is also attached to the chassis?


Is it advisable to run 3 wires: (1.) positive (red) from the battery (2.) negative (blk) from the battery (3.) a ground cable 18" inches or less 1" flat ribbon to chassis at the location of the radio in the       trunk?

"40 Years of HF Mobileering" is no longer in print ( In addition to answering my questions here, would you provide other recommended sources.

              John (Mobile Wanna Be)
              73's de KB3CDF

« Reply #1 on: January 10, 2001, 07:32:41 PM »

hi there,

You should use seperate wires to battery
directly, fuse on both pos and neg cable.

The battery acts as a filter and helps keep
out alternator whine.

By going to battery directly, you avoid power drops
from car items (a/c clutch, fan, heater, etc)

The neg fuse is just in case there is a problem
with your car wiring and will not let high amps pull
directly from your radio (starter for example).

Remember, copper is better conductor then steel.
So you wire direct to battery.

You should be able to run power from battery
and follow along the hood release cable to feed
into car and along to the rear of vehicle.
That way you do not need to drill more holes.
Be sure to protect cable from car sheetmetal where
you pass into the car.

good luck.


Posts: 145

« Reply #2 on: February 02, 2001, 04:31:08 PM »

Use at least #8 wire.  I agree with the above post on running two wires.

Using the chassis for ground is poor advice.  Often the negative wire between battery and chassis is not very heavy. The connection to the chassis is only for lights and accessories. The starter current is handled via a large (#4) battery cable directly from the battery to the engine block.  Also, running high current through the chassis can cause corrosion at the grounding point.  Additionally, you can pick up noise from currents flowing via the car's body.  (Look up "ground loop").

I suspect that those audio "specialists" are just trying to save money on wire.

« Reply #3 on: September 10, 2001, 12:35:48 AM »

I'd say just run one wire and ground to the car body.
Look at how many thousands of emergency vehicles out there ground to the body.
About 97% of all the Motorola trunk mount radios are grounded at the body.

My personal vehicle is setup with three 110 Watt Motorola Syntor X9000's.  these are trunk mount radios. They are all fed of one large B+ lead direct from the battery. Have ran this setup for years, no problem.
granted, I dont run HF in the mobile, but I'd try the single wire, if it works...go with it.
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