Just in time to aid in diagnosing your suddenly sick Series 3, you can get a free digital multimeter.
Look in your Sunday paper today (October 20, 2013) for the Harbor Freight Tools circular.
(It probably helps if there's a Harbor Freight retail outlet in or near your community.)
There's a coupon in there for a free meter.
(You do have to actually go into the store with the coupon, but you don't have to buy anything else)
Remember when calculators that only did the basic 4 functions (+, -, *, /) sold for several hundred bucks and now you can get one for $2.95 or maybe free inside your breakfast cereal?
Well, same trend has happened with digital multimeters.
So cheap doesn't necessarily mean worthless.
Get up with someone else getting one of these and put one on DC Volts and the other on resistance/continuity and see what the polarity is of the current the second one uses to test resistance and continuity, so that if you ever need to know, you already will.
In the old days of "analog" moving needle meters, the red lead, usually thought of as the "positive" lead because that's the one you used to make contact with the positive terminal of a direct current source, became the source of "negative" electrons when switched to the Ohms function, and the black lead, usually "negative" when measuring current or voltage, became the return path for those electrons, so that the negative lead was positive and the positive lead was negative.
Not doing it that way would have made switching from Volt/Amp functions to Ohm functions more complicated.
Most digital meters these days, when putting out current to measure resistance and continuity, make the black lead the source of electrons and the red lead the more positive return path for them.
But I can't swear that they all do, so it's a good idea to check it in advance so that you'll know if you ever need to.