Which side negative? Autos

I have an expensive auto compass -- but I've lost the instructions -- with a wire in which both halves are black, but one side is marked with grey or white rectangles. Which one is the ground?
Thanks
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which way works?
randy

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meirman wrote:

Try both. Low voltage DC, you wont damage anything. The one that makes the compass point the right way I assume is the correct one. Also consider that its for a light or something and it does not matter.
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Respectfully,


CL Gilbert
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In alt.home.repair on Tue, 02 Aug 2005 10:24:00 -0400 "CL (dnoyeB)

It's both for the light and the guts.
I was doing wiring now, and hoping to solder the wire in place while the compass itself waits for me to make a bracket to hold it in place**.
But you're right, I can hook it up while it dangles from the dash and see what it does.
** The new dashboard is practically vertical. I have to make a complicated bracket, at least 4 bends. Not even sure how wide I want the bracket to be, so I'm stalling.
I went back to radio shack where they used to sell this, to remind myself how to set north and south, but they didn't have compasses or this model anymore. I think I remember how to set north and south though.
I bought a lot of car compasses over the years and this is the first to work. 30 years ago I wrote to AirGuide and asked them if I bought a more expensive compass, would it work, and they wrote back that they were all the same and sent me more double sided tape to try new locations.
Since then I once had a 3/4inch plastic sphere, that came atttached to a convex rear view mirror clip on, that worked. It only cost a dollar. Eventually the water drained out. Another that looked the same, but had a suction cup didn't work. Maybe the prior car had an unusually balanced or absent magnetic field where the compass was.
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An electronic auto compass may NOT be protected against reverse polarity. Try finding the manufacturer online and maybe they will have the instructions online,or will send you a copy,or tell you in an email.
It would also help if you posted the *make and model info* and any numbers on the case,maybe someone here has the same item,and can help.
Also try rec.autos.driving or other auto-related NGs.
--
Jim Yanik
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Most likely the side with the rectangular markings is negative. Batteries have + (positive) and - (negative markings)

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In alt.home.repair on Tue, 02 Aug 2005 16:26:22 GMT "FDR"

You're the winner!
"Cut the cigarette lighter plug off of the power cord. Connect the wire that does not have a stripe to the +12 volt power source ....
Connect the wire that has the white stripe to a good ground source."
It did warn about heat damage if I used a fuse over one amp, but didn't warn about connecting it backwards. But people do use larger fuses at times. OTOH The instructions on how to connect the wires are quite clear.
I didnt' think I'd be able to find the notes online but I did. It was sold by Radio Shack, but I had bought one just like it from somewhere else. So I didn't have a part number. But I went to the manuals section of RS's website. And then to auto, and then to auto accessories, but all they had were antennas and radar detectors. So I was disappointed that the manuals section seemed to only give currently sold stuff.
But there was also a Search field, and that brought up 102 entries over 14 pages. One that sounded right was on the first page, and when I checked it had about the right date, and the right instructions for setting north and south, which I pretty much remember but I'm very glad to have. So I had it.
I went to the basement and saw that it was Radio Shack after all. I didn't buy the other one. But it had no model number. But it did say Flux Gate, which would have made the search quicker.
Thanks to everyone who tried to help.
(I thought this would be a simple question, not requiring going beyond the wire.
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meirman wrote:

That would have been my guess based on lamp cords, etc., but only a guess...
Don't suppose there was any indication if you tried resistance check between case and the two leads to see of one showed a ground connection? (Not that it matters now, of course...)
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In alt.home.repair on Tue, 02 Aug 2005 15:00:00 -0500 Duane Bozarth

I think the case is entirely plastic.
Thanks.
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I feel ripped off here;I posted this at 11:27AM EST; An electronic auto compass may NOT be protected against reverse polarity. Try finding the manufacturer online and maybe they will have the instructions online,or will send you a copy,or tell you in an email.
It would also help if you posted the *make and model info* and any numbers on the case,maybe someone here has the same item,and can help.
and Duane gets all the credit. ;-(
TANJ. :-)
--
Jim Yanik
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In alt.home.repair on 2 Aug 2005 23:54:51 GMT Jim Yanik

He's the winnner of those who said plus vs. those who said minus.

I saw your post, but I was sure I had a version with a brand that was gone by now. It seems we're talking about 1997. ;)
I was quite urprised it was RS.
But you are the winner for good advice.

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Marked wire is usually positive...
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Rick wrote:

And FDR says the marked wire is most likely negative...
Any other guesses, anybody? :)
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I agree that the marked wire would be positive, since normally in the electronics/low voltage world, black == ground, and modern automobiles are negative ground. Since the wire is black, the marked lead would be positive.
Even when the wire is not black, the convention seems to be that the marked lead is positive, unless the marking is black colored, such as red zipcord, with one conductor striped with black.
This holds true for both colored stripes, and physical markings (ridged conductor on zipcord.)
I've never encountered a device with a black cord, where the marked lead was negative.
While the device may be protected against reverse polarity, there are exceptions, and the exceptions will probably let the smoke out in the process.
One quick test might be to check continuity between the power leads, and any metal chassis of the device. continuity == negative side.
Is there a fuseholder in this cord? they are normally found in the positive lead, except for some high powered equipment (ham radios, etc) that are intended to be run directly to the battery, which are frequenty fused in both leads to prevent the radio from being the primary ground path in the event that the main bettery-chassis ground becomes disconnected.
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-- Welcome My Son, Welcome To The Machine --
Bob Vaughan | techie @ tantivy.net |
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The one that connects to the negative terminal.
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Larry Wasserman Baltimore, Maryland
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