On Sun, 14 Oct 2018 10:26:55 +0100, Jeff wrote:


I inspected the electrical system and found that fuse on the negative
lead had blown. Why manufacturers persist in providing a negative
wire fuse will remain a mystery as there are very few positive ground
vehicles still in service and even marine radios with floating grounds
are scarce. I have no idea where the radio was getting its ground
return for reasons that will soon be obvious. I replaced the fuse and
continued looking for problems.

The negative fuse is nothing to do with positive ground vehicles (and a
radio with the case connected to negative would not work in a positive
ground vehicle anyway without additional isolation).

The negative fuse is there to stop high currents, such as the starter
motor, being drawn through the radio wiring and coax should the battery
to chassis connection be high resistance or open circuit, and prevent a
possible fire.

This is at greatest risk if the radio negative is wired directly to the
battery.

Jeff

That seems reasonable. However, I've never seen that happen.

More common was blowing or removing the negative power cable fuse to
the radio. That makes the DC ground return for the radio go through
either the car frame, which will produce alternator noise on the
transmit signal, or through the coax cable, which will produce a
smoking coax cable in transmit. I've seen both about 5 times each in
the last 50 years. I would consider these faults to be a greater risk
than a disconnected battery to chassis (or engine) ground cable.

"Wiring and Grounding"
http://www.k0bg.com/wiring.html
And as shown, the negative lead fuse should not be removed.
The reason is, if the grounding point should lose its integrity,
excessive current could flow through the transceiver's
negative lead. It also prevents a minor ground loop between
the leads.

Most vehicles have a ground strap between the engine block and frame
and another ground cable between the frame and negative battery
terminal. I sometimes see a third cable from battery to engine block.
In this arrangement, any one of the three wires could be disconnected
and one would still have a tolerable grounding system. Fiberglass
body automobiles have duplicate ground wiring since there is no frame
ground.

"How To Properly Ground An Automotive Electrical System"
https://www.hotrodwires.com/how-to-ground-automotive-electrical-system.html

"Is it necessary to have two ground wires (1 to engine and 1 to"
car-frame)?
https://mechanics.stackexchange.com/questions/5903/is-it-necessary-to-have-two-ground-wires-1-to-engine-and-1-to-car-frame

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

In article ,
says...

The negative fuse is nothing to do with positive ground vehicles (and a
radio with the case connected to negative would not work in a positive
ground vehicle anyway without additional isolation).

The negative fuse is there to stop high currents, such as the starter
motor, being drawn through the radio wiring and coax should the battery
to chassis connection be high resistance or open circuit, and prevent a
possible fire.

This is at greatest risk if the radio negative is wired directly to the
battery.

Jeff

That seems reasonable. However, I've never seen that happen.

More common was blowing or removing the negative power cable fuse to
the radio. That makes the DC ground return for the radio go through
either the car frame, which will produce alternator noise on the
transmit signal, or through the coax cable, which will produce a
smoking coax cable in transmit. I've seen both about 5 times each in
the last 50 years. I would consider these faults to be a greater risk
than a disconnected battery to chassis (or engine) ground cable.



I don't know anything about the tractor trailer wiring, but around 1972
I picked up extra money repairing the CB radios. Several truckers
brought in rigs that were blown up when switching from the car to the
truck. None of them had a fuse in the negative power lead. By blown
up, most had a diode across the poer wires inside the transceiver and
that diode had shorted and blew the fuse. I seem to remember then they
talked about the tractor haveing a positive ground. Probably ran on 24
volts also.

I have only ran FM ham rigs in a car. I used to ground the rig to the
frame and run the positive to a relay that comes on when the car is
started. Never had any alternator whine or problems. For about the
last 10 or more years I just plug into the lighter or accessory socket
in the car. My Toyota power on those sockets only come on when the car
is started.

On Sun, 14 Oct 2018 13:39:38 -0400, Ralph Mowery
wrote:

I don't know anything about the tractor trailer wiring, but around 1972
I picked up extra money repairing the CB radios. Several truckers
brought in rigs that were blown up when switching from the car to the
truck. None of them had a fuse in the negative power lead. By blown
up, most had a diode across the poer wires inside the transceiver and
that diode had shorted and blew the fuse. I seem to remember then they
talked about the tractor haveing a positive ground. Probably ran on 24
volts also.

I installed a few radios in White Freightliner tractors in the 1960's.
They were all positive ground 12V. I think they switch to negative
ground in about 1975. Many other older tractors were positive ground
but switched to negative ground in about 1954-56. I vaguely recall
conversion kits being sold at the time.

I've seen a few 24V electrical systems, but those were all in military
vehicles.

I have only ran FM ham rigs in a car. I used to ground the rig to the
frame and run the positive to a relay that comes on when the car is
started. Never had any alternator whine or problems. For about the
last 10 or more years I just plug into the lighter or accessory socket
in the car. My Toyota power on those sockets only come on when the car
is started.

You might want to put a voltmeter across the power connector going to
your radio and across the battery, and compare voltages in transmit.
Methinks you'll find a rather substantial voltage drop through the
cigarette igniter jack. Also, that connector was never designed to
handle a plug and jack connector arrangement. It's the only connector
that I know of that has a spring which pushed the plug OUT of the jack
and lacks a retention system.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

In article ,
says...

I installed a few radios in White Freightliner tractors in the 1960's.
They were all positive ground 12V. I think they switch to negative
ground in about 1975. Many other older tractors were positive ground
but switched to negative ground in about 1954-56. I vaguely recall
conversion kits being sold at the time.

I've seen a few 24V electrical systems, but those were all in military
vehicles.

I have only ran FM ham rigs in a car. I used to ground the rig to the
frame and run the positive to a relay that comes on when the car is
started. Never had any alternator whine or problems. For about the
last 10 or more years I just plug into the lighter or accessory socket
in the car. My Toyota power on those sockets only come on when the car
is started.

You might want to put a voltmeter across the power connector going to
your radio and across the battery, and compare voltages in transmit.
Methinks you'll find a rather substantial voltage drop through the
cigarette igniter jack. Also, that connector was never designed to
handle a plug and jack connector arrangement. It's the only connector
that I know of that has a spring which pushed the plug OUT of the jack
and lacks a retention system.



Ok on the tractors being 12 volts. As I mentioned I did not know the
voltage but thought they were positive ground as the truck drivers kept
blowing the transceivers up when switching from the car to the tractor
and back again.

I did not put the voltmeter on the car,but a wattmeter shows the
transmitter is giving close to what it is suppose to put out. The
accessory jack is rated for 10 amps . This is for a transceiver that is
rated for 50 watts out.

I did melt out one of the inexpensive lighter plugs. It was made of
soft plastic instead of the hard type.