[TR] Positive or Negative Earth

[Randall]

---- Dave <dave1massey at cs.com> wrote: 
> You don't have a voltmeter, you say?
> Well, you should if you plan on 
> doing any electrical troubleshooting.

If you own an old car, you should have a meter even if you don't _plan_ to do any troubleshooting!

Digital multimeters (which will function as voltmeters) have gotten so cheap, and so rugged, that there is no excuse not to have one in every old car you own.  Harbor Freight almost always has one or more of them on sale for under $10; at the moment I count 3 different models under $10.

If that's too much, check out eBay.  Here's one for $5 with free shipping in the US.
http://goo.gl/005R2n

Not as accurate as more expensive models, but way better than nothing.  And if it breaks, just buy another.

There's also a way to do it with a couple pieces of copper wire and a potato, but I haven't tried it since high school and might not remember all the details.  As I recall, you cut the potato (to make it easier to see), sprinkle a little salt on it and jam the wires in fairly close to each other but not close enough to touch.  The potato will turn green or yellow around one of the wires; that's the positive wire.

Be sure to discard the potato afterwards.

Randall