[fitchn]

Test the resistance between places that should be ground (like a wire connection or whatever) and someplace that you know is ground, like the negative battery terminal. While observing the resistance, vigorously stress/shake the connections and wires between that location and ground looking for a change in resistance. Most multimeters have a beap feature that makes a sound when the two leads are in "contact" through a circuit, you can use this to just listen for the beap to stop while you wiggle, instead of watching the readout. Keep in mind that the contact resistance of the meter will probably read around 0.1 ohms when the two leads are connected through a wire, take this as zero. A broken circuit will read some very large resistance (many mega-ohms) or the gauge won't read at all. Hope that makes sense and good luck.