How do I tell positive from negative wires?

I have a new GPS unit on which I need to shorten the power cable. The cable has a USB plug on one end. The USB plug fits into the GPS unit.
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When I cut the power cable, one set of wires is incased in a white plastic/rubber sheath. I assume these are positive but I am not sure.
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The other set of wires were bare. No sheath, other then what encased the power cable as a whole. I think this must be negative but I don’t really know why I think that.
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Can anyone here enlighten me?

Negative wires just never have anything nice to say.

want to share a pic? Might help.

type "(name of my gps) pin out" into you browser... as in "Garmin Nuvi pin out"

Is it a coax type cable, ie does it look like the cable to your tv wire? Then the positive wire would be the center and the ground on the outside. I never cut a usb cable so I'm not sure what they look like inside.

I'l bet you even cut classes in school didn't ya.

do your parents know you are using their internet hookup? They WILL find out you know,,just sayin',,you might wanna think about,,

No, USB is usually 2 to 4 conductor cable. Coax would be really wacky for that usage. But yeah, this thread is smelling like the one where the kid burned up two GPSes because he didn't know 5v was different than 12v...

Ask your kids about punctuation, Peterman

Yep, I sure did. Now I am retired with a good income, how about you?
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Thanks for the help guys

The Garmin manual that came with my new unit had a diagram in the last few pages that showed which of the pins were for power/ground. Index had the page number when I went looking for it.

Maybe you should have just coiled the excess cable out of site and secured it with a couple of wire ties. GH

I wanted a short power cable that I could just unplug when I removed the GPS from the bike. That worked very well for me with my deceased GPS unit.
The way this new power cable is designed I can not just fold it up to shorten it as much as I need too. And apparently with a USB plug the cable shouldn’t be shortened as I had in mind.
Hopefully, I’ll know more Monday.
I am not going to post anymore in this thread. I never expected to meet grammar Nazis in the Garage.
For those who tried to help, Thank You.

Don't hardwire that USB cable from your GPS to your bike. USB cables are for a 5 volt systems, you will ruin your GPS the first time you try to put power to it.

Ok but just because it has a usb end doesn't make it a usb cable. If it was a power cord for a 12v system you should be able to shorten it to your desired length. That is why I asked what it looked like inside. I have phones that have a similar looking plug to a usb,but they only have 2 wires, the rest are dummy terminals. Can you buy a short lead from say Touratech for your unit, and not risk damage to your new unit?

Apparently it's too hard to give us more information so we can solve his problem for him.

Yep, the positive wires usually are more upbeat.

It depends on what GPS unit you have. Some will handle as much as 36 volts but other will fry if fed more than 5! Many power cables house the voltage reducer in the lighter plug but it could be anwhere on the cord. GH

was there a cig plug on the utter end of the power cord?. if so there's a fairly recent thread about cutting off the cig plug and the problems that ensue (spelling police please take note- your powers are weak)

Not if they are USB cables, bubba.