Jack3000 wrote:

In general which wire is usually positive? The wire that has the
writing on it?

A dirty little secret about wire is the fact that it is rarely if ever
marked with pluses and minuses.

Some cables are even composed of two absolutely identical wires. Nasty, eh?

Most wire has some distinguishing marks, such as the writing that you've
noticed. Or, there is a color difference. Or ,there is some texture or
ribbing molded into the insulation. Or, one conductor is plated and looks
silvery, while the other is unplated and is copper-colored.

In some cases the difference between the wires in a cable is gross, such as
shielded cable where one "wire" is the stranded shielding braided over the
other wire, which is more conventional.

The second dirty little secret is that in most cases it doesn't matter which
wire you consider to be plus and which wire you consider to be minus, as
long as you are consistent with your choices at both ends of the same piece
of wire.

Often with wire, nobody cares about your choices but you, but you should
care very much about your choices.

If your memory tends to fail you, cut up some pieces of say masking tape or
bandage tape, use an indelible pent to write positive and negative on them,
and apply them to both ends of the wire when you can easily see both ends
of the wire at the same time. Again, be consistent!

If you do this often, you can even get little books of adhesive markers at a
home improvement or electrical supply store. They tend to fall off as they
age, so real neatnicks hold them in place with clear shrinkable plastic
tubing.

One common exception to the "don't care" rule is the black, green, and
white wiring that the AC wiring in your house is probably made up with, if
you live in the US. Black is "hot" (call it plus), white is "cold" (call it
minus), and green is safety ground. For reasons of safety, everybody who
wires houses follows this standard for assigning function to the various
colors of AC wiring.

So, if one wire in a cable has printing on it, and the other doesn't have
printing on it, then make up your own mind about which is positive and which
is negative, but be consistent.

If you need more help, I say (flipping coin) make the wire with writing on
it be unhhhhhhhhhhhhhhhhhhhhh "positive".