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Strange Wire

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ron wilson

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Just bought a (project 74 MGB) The owner prior to the one I purchased it from had installed a sterio system and had a wire running directly from the sterio to the positive post on the battery. Why would someone do this ?? My only guess is that the polarity of the sterio ldoes not match that of the vehicle and this was done to get around that problem????
 
Modern digital stereos have what's called a "memory wire". It is an unswitched power source that retains the clock setting and presets when the ignition is turned off. That's probably what that wire was. But it would be a lot easier to tap a hot wire in the dash for a future install.
I hope there was a fuse somewhere in the wire.
 
You could tap a hot wire under the dash without going all the way to the battery, but if you use a battery cut-off switch, you will lose the memory every time you use the cut-off switch.
 
[ QUOTE ]
You could tap a hot wire under the dash without going all the way to the battery, but if you use a battery cut-off switch, you will lose the memory every time you use the cut-off switch.

[/ QUOTE ]

Both make sense to me, except if you use the battery cut off on the negative terminal and you run a seperate wire to the ground post for the radio, you will end up grounding the entire car through your radio /ubbthreads/images/graemlins/crazyeyes.gif
And God help you if you forget to connect the ground side and hit the starter, jamming all that juice through the acc circuit and back to the battery through that little wire /ubbthreads/images/graemlins/blush.gif

Bruce /ubbthreads/images/graemlins/cheers.gif
 
That little wire for the memory should be fused just like the main power for the stereo.

The starter should get its current directly from the big cable/lug on the solenoid. Unless he's got other devices connected to that solenoid terminal, trying to start the car with the battery disconnect switch "open" won't create a situation that will try to feed the starter.
 
Feeding the starter is not a problem as the positive terminal is connected normally...but if the disconnect is hooked to the ground terminal (as most applications are) and the only wire to the battery negative side is a thin ground wire from the radio to the battery (to keep the settings set and clock running when the disconnect is open) wouldn't the only ground to the entire car be through that little wire? And if you run anything, including the starter, wouldn't it fry that little ground wire?

Bruce
 
"Fry" may be a bit of understatement... ever see an LBC after engine/trans have been out and the ground strap(s) left off? Throttle & choke cables become a "bit" FUBAR'd at best.

The radio'd be toast, albiet with less "drama" methinks. It'd happen in an eyeblink.
 
I see your point about damage if the disconnect is in the battery ground cable.
 
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