Black wire in the middle connector, red in the right. To measure voltage, stick it to 20V (to see if there's anything coming from the feed wire to the indicator). To measure resistance, you'll need it on 200Ohm - about 6 o'clock (to measure the resistance of a wire/bulb etc or find if you've got an iffy connector). You can extend the wires with... another bit of wire. The only thing you'll have to be mindful of is that if you've got it on Ohm then you'll need to account for the additional resistance of said bit of wire. You don't have to use the battery -ve, any bit of bare metal on the frame should do.