USB Port

nimrod · 2026-04-14T08:08:20-0600

Hi all, I want to fit a USB port onto my mk3 1976 roadster, for reading GPX files ie routes, on a rally I am going on in a few weeks time,
the connection cable has a red and a black wire with a one way only plug to connect to the USB cable, making sure red to red etc. other end has eye connectors for battery connection, my question is which way do I connect to the battery as its a positive earth making red earth/black positive. I think on switches etc it wouldn't matter but I have no understanding what or how USB works. I don't want to wreck my phone. Help required please.

kommando · 2026-04-14T08:47:23-0600

The USB socket is 5V, does your assembly take the 12V and present only 5V at the USB socket ?

When I did mine which included a 12V to 5V dropdown circuit then red went to positive and black to negative. Does not matter how the battery is wired pos or negative earth, red goes to +ve black to -ve.

nimrod · 2026-04-14T09:23:54-0600

kommando said:
The USB socket is 5V, does your assembly take the 12V and present only 5V at the USB socket ?

When I did mine which included a 12V to 5V dropdown circuit then red went to positive and black to negative. Does not matter how the battery is wired pos or negative earth, red goes to +ve black to -ve.

yes it should drop, not sure how I check that but I am sure it happens inside the black box., thanks for the connection info, makes sense that way but looked odd.

kommando · 2026-04-14T09:27:21-0600

You can take an old USB cable and cut the male plug off with a foot of cable, strip to the internal wires and then plug into the socket and put a multimeter onto the internal wires looking for 5V. The are pinouts online telling you the colours of the internal wires and what they mean, but they are guidelines only as I found when testing once to find + and - reversed

, only the Chinese could do such stuff. Before I took it apart it worked so they reversed it at both ends.

concours · 2026-04-14T09:35:32-0600

Battery Tender USB Charger - RevZilla

This nifty little doodad plugs right into your SAE battery harness for easy charging of your iPhone, iPad, iPod, GPS, camera or any smartphone or devi…

www.revzilla.com

Mark Savage · 2026-04-14T09:57:08-0600

I fit one of these to my battery charge lead when needing a USB port for topping up my phone. https://www.sportsbikeshop.co.uk/mo...BWrpT7jIdQFysxtvUKku7KZS91ik0n8YaAg9pEALw_wcB

Fast Eddie · 2026-04-14T10:08:09-0600

Mark Savage said:
I fit one of these to my battery charge lead when needing a USB port for topping up my phone. https://www.sportsbikeshop.co.uk/mo...BWrpT7jIdQFysxtvUKku7KZS91ik0n8YaAg9pEALw_wcB

That’s a nice little gadget !

Schwany · 2026-04-14T10:12:23-0600

Have fun on the rally.

Made me look. Type USB Charger into google and hold on to your butt. There are a zillion of them. Most if not all of them are made in China.

The ones with the amp and volt meter look interesting, but would a hardwired (no switch) unit drain the battery on a bike parked for several weeks?

concours · 2026-04-14T10:19:43-0600

I use this continually, as I run the Wazeapp continually. It gobbles battery.

ludwig · 2026-04-14T15:47:13-0600

I have a USB port on my N15.
(the knob on the right is to adjust the head light)
The voltmeter normally shows 13.5 V when riding.
When a device is plugged in, usually GPS, it indicates 5 V.

USB Port

Similar threads