Just some useful information for anyone considering carrying out the fitting of a USB port to the storage box to enable a simple and easy connection to a sat nav unit. This applies mainly to Garmin units but may apply to others as well.

Garmin use a customised mini USB port to enable the unit to recognise the difference between a PC and a charging/power unit. on a mini USB there a 5 pins labelled 123X4 normal USB connection have 1 to +V 4 to 0 volts 2&3 are data pins the colours are 1 red 2&3 green and White 4 black. X is not connected.

Garmin charging plug USB plug is as follows 1 +V 2&3 no connection 4 Grounded to plug casing (the metal bit) and the X connection is connected to pin 4 via a 27K resistor within the plug moulding.

This is a standard method of providing device recognition when using USB devices not garmin being sneaky.

The upshot of this is that you cannot use a standard USB lead or the PC lead provided by Garmin to connected to your in-car charger and power lead as the unit will think it is connected to a PC and not switch into nav mode.

Garmin charging plug USB plug is as follows 1 +V 2&3 no connection 4 Grounded to plug casing (the metal bit) and the X connection is connected to pin 4 via a 27K resistor within the plug moulding.

This is a standard method of providing device recognition when using USB devices not garmin being sneaky.

Thanks for that - that's really useful information

I guess the easiest method is still to hardwire in the standard Garmin charger, which is what I did. Just got myself a female cigarette lighter adapter and wired it into the fusebox, plugged in the standard Garmin charger and buried it all behind the dash with just enough cable and connector protruding to allow it to be connected to the SatNav. The upside is that it's a cheap and largely reversible mod.

What is still useful is one of those small USB adapters that fit in the cigarette socket for use in the 12v socket in the boot - great for charging any number of devices with a USB lead when you're away from the car, locked securely in the boot and out of sight. BTW, I think I read recently that the mobile phone industry had recently agreed to standardise on those mini-USB connectors for charging too so hopefully within a year or two you'll be able to charge just about anything from a USB socket.

Surely they must manufacture a standard USB lead to permit charging from the plethora of usb chargers out there? When I say "they" I don't necessarily mean Garmin.

Any harm in wiring the usb output plug appropriately so that a normally USB cable can be used? What will this do to other usb devices?

But what if you plug the lead into the bracket for the Garmin (I have a 1690) and not the actual unit itself? I think the bracket will strip out the data and only feed power to the unit?

Just tested it, it works. So go ahead and build a USB port into your storage bin if you have a Garmin 1690 (other units too?) and use the provided bracket.

But what if you plug the lead into the bracket for the Garmin (I have a 1690) and not the actual unit itself? I think the bracket will strip out the data and only feed power to the unit?

The information I provided assumes that the power lead is fed strait through to the Mini USB I have no information about any brackets and did not get one supplied with my 1490 unit.

Surely they must manufacture a standard USB lead to permit charging from the plethora of usb chargers out there? When I say "they" I don't necessarily mean Garmin.

Any harm in wiring the usb output plug appropriately so that a normally USB cable can be used? What will this do to other usb devices?

THe USB outplug plug cannot be rewired because it is a moulded plug and the internal connections to pin X cannot be accessed

Ah, on the 1690 the provided bracket has a mini USB input on it, that means you only need to clip the unit in place and it is immediately powered.

Here you go - http://briskoda.net/forums/topic/155009-has-anyone-installed-a-cigarette-socket-in-the-top-dash-box/page__st__20__gopid__1942467entry1942467