Peter
The earth wire from the radio unit is really there to make a more solid
ground. You are probably also earthing through the aerial, and the radio
case is probably grounding to the battery as well especially on older cars
where units are mounted to a decent bit of metal, unlike modern cars.
Anyway, your wire to the radio is creating an earth that anything will
attempt to use to complete the circuit, so your lights will work - to a
fashion, but the starter motor will have no show as the circuit has would
have far too much resistance. The wire will get hot attempting complete the
circuit though.
In summary, if you could guarantee that your radio is completely isolated
from the body (which acts as the common ground), then your separate earth
idea would work, but the complete isolation would take a heap of work to
achieve...
David Greed
1979 2500S Man O/d
Email: greed@wave.co.nz (Home)
sys_dwg@cmosaf.telecom.co.nz (Work - AlphaStation)
david.greed@telecom.co.nz (Work - PC)
-----Original Message-----
From: Peter Zaborski <peterz@merak.com>
To: 'TR6 List' <triumphs@autox.team.net>
Date: Saturday, 4 April 1998 19:07
Subject: wiring oddity
>
>This one has me stumped at present...
>
>I recently installed one of the battery cutoff switches (as seen in the
>Moss catalog for around $12). Basically you mount the switch on the neg
>post and attach the ground cable to the other end of the switch. In the
>middle is a threaded knob which when loosened, breaks the connection
>between the two halves of the switch. Very handy since I always seem to
>be disconnecting the battery for something. This way I don't have to
>remove the clamp from the post. Works just great and as a bonus,
>removing the threaded knob outright acts as a "crude" theft prevention
>device.
>
>Ok that's the background - now here's the stumper...
>
>I also have a stereo which has an electronic clock and presets for the
>radio stations stored in its memory. Of course each time the battery is
>disconnected these settings are lost. Clever me, I thought I would
>outsmart Mr. Battery switch by hooking up a ground wire from the neg
>terminal of the battery to the ground of the stereo directly.
>
>(I should mention that the stereo is wired so that it has two power
>connections - one for when the ignition is on for normal operation, and
>another connected full time to the brown terminal on the fuse box. This
>also works correctly.)
>
>Now when I disconnect the battery using the switch, it doesn't really
>disconnect. I can turn on the lights which is something I could not do
>before installing the "custom" ground wire. The lights go noticeably
>dimmer than when the switch is connected, but they do stay on
>nonetheless. Something is allowing the battery to get grounded through
>the stereo.
>
>Anyone have any ideas on what is causing this? And more importantly, how
>can I resolve this as I would definitely like to have the stereo
>isolated form the action of the switch if possible.
>
>Thanks for any insights into this little puzzler,
>
>Peter Zaborski
>76 TR6 (CF58310 UO)
>Calgary AB Canada
>
>
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