Don't have the actual unit, but I can help with the maths - so you can work it out - I think..
W=IV (W= watts, I = current & V = volts)
Therefore I=W/V. Knowing the voltage of your a/c (12v?), look at the power consumption (in watts) of the unit (almost always printed on the back, or maybe available in technical specs on the web). Plug the numbers into the formula above and you will get the average current. Add say 25%-50% and get a fuse at that rating.
(PS It was a long time since I did my Physics at school, so if anyone spots a problem with above, feel free to enlighten us!)
PPS I'm guessing your unit may draw up to 1w (My GPSIII handbook quotes 0.5w max). So using the above formula, I'd be looking for a fuse aroung 0.1A -0.2A. I'm sure there wouldn't be a problem going for a bigger one - the main thing is to stop a fire if your unit packs up and I can't see one starting with such small currents (+ you'd see it pretty quick yourself)
Last edited by down&out; 9th Sep 2003 at 03:17.