14-08-13, 07:55 AM
II hadn't twigged that you'd disconnected the negative terminal when you got that 12v reading.
Andy FZS is correct, the speedometer is still powered even when the ignition is off (which is why when you disconnect the battery your tripmeter goes to zero) so that path may have been enough to give you the reading you saw.
Rather than trying to make readings of current (I find it's easy to absent-mindedly short things out that way) I'd stick to the voltage range. Just measure the voltage across the battery while you turn the lights on, if the voltage plummets it's a sulphated battery, if it holds up and the lights don't come on it's loose or dirty connections somewhere.