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[Frank]

Not any old cig plug but one that gives out 5v for charging. You can get small plugs with usb sockets on them that you can connect a usb to micro usb lead to. they are less likely to vibrate out than the bulky items that are fitted to the supplied charging leads. The one that is fitted to my car you have to rip your finger nails off trying to prise it out. You can get them with either a single or dual usb socket outlet, should you wish to charge a phone up at the same time I guess.

[Exile]

OK.. revised circuit diagram..





I had a look at the GPS screen unit. It is rated at 5v and 2 amps. The screen unit mounts on a base unit. No markings on that but I think it must contain some kind of regulator to reduce the ingoing voltage to the screen unit.


Now, does this make sense.. Using the voltmeter across the switch with the switch off, I still measure 6,8 volts. Adding 6,8v to the 5v, we get 11,8v.

That's as near as damn it to 12v as you'll get allowing for all the junctions, cable resistance and other variables.


Or have I lost it completely...?

[Frank]

Ok so are we saying that there is no wires going into the gps unit itself but the wire from the battery disappears into the base unit and the gps picks the power up from contacts on the base unit? If so can you measure the voltage on those contacts?

[Frank]

Based on your new diagram, if that is how it is set up now, and you get 6.8v at the switch then all is well to there. The output from the plug needs to be 5v at a 12v I/P but since the battery will be marginally higher than 12v say 12.6-13v then the output will be a bit higher i.e 6.8v. The important thing is what is it at the last point it goes into the gps. If it is 6.8v there and the unit is stamped 5v then it is ok.

[Exile]

Thanks Frank. So I'm not yet completely barking mad...

I suppose that I will have to take it out and test it once again to see if the new set up helps.

If not, then I will drop the whole GPS idea.. I'd rather be lost than be stranded on the roadside.
😆