Tom toms can need 1.2 amps, if your motorcycle usb adaptor only does 1A then the Tomtom internal battery will be slowly discharging and eventually going flat usually at the most inconvenient time. As others have said a genuine Tomtom adaptor or a high power 2.1A cigarette lighter to usb adaptor can be cajoled into working at 6v.
We had the same problem last year travelling through Europe in a vintage car but usually it was my fault as I had knocked the lead out, but you are right, inevitably when entering a roundabout.
My TomTom would only need need 1.2A if plugged in with a very flat battery. It very soon charges up while in use. Once the initial charge is complete I imagine it will only draw milliamps while in use. On mine the battery lasts for several hours use on a full charge without being plugged in. The ARM 9 processor is very efficient, screen illumination is LED.
thanks for your input guys, I will purchase a cigarette socket and hot wire it to the 6 volt battery. I have with me a tom tom cigarette lighter plug with usb female connection. I do believe that the motorcycle usb port is of sufficient amperage, but the operation seems dodgy. I'll let you know how it goes.
Seems a big day today we are now in the North York Moors National Park having travelled about 100 miles, I'm in the local pub and I believe they are speaking English but there's nowt I understand! cheers Russell
Location: back in the UK in Primrose, going to guildtown !