TESTING CONTINUITY WITH THE MULTIMETER

One of the most useful tools in the box for sorting out wiring and cabling problems  is the continuity feature of your multimeter. On most meters it is marked with a small arrow. When selected, if you touch the probes together, the meter should make a sound - usually a beep - this means "short circuit".

Not all meters have this beep function. Most modern ones do, and if you are going to buy a meter, make sure yours does. On meters without the beep, then you have to use the "Ohm" setting, or "Diode" setting which will display zero on the meter display when you touch the probes together. 

So to test a connection, you touch one end of the wire with one probe, and the other with the other probe, and if you get a beep, then that proves there is "continuity" along that wire.

So if you have a bunch of wires at 2 ends, and no idea which is which, you use this feature to identify which is which. Attach one probe to one wire at one end, and then touch the other probe to each of the others until you get a beep.

But you have to remember that one end of the wire being tested is free - ie open circuit. You can't use this technique on connected wires, because there may be a path through another part of the circuit that will give you a false reading.

If the meter leads are too short, then you simply extend them using a long piece of wire, suitably connected - can be as crude as wrapping and taping. You check that you have a good connection by simply touching the probes together.

This technique is also useful for identifying grounds. DC current flows from pos to neg, with neg being chassis ground. If the ground neg wire or connection is not a solid path, then the circuit will not complete. So when testing and troubleshooting, you have to be sure that the neg has a good path to ground. The way to do this with a meter (set to continuity) is to attach one probe of the meter to the negative terminal of the battery - because that is 100% guaranteed to be the neg ... and then the other probe to the neg wire in question. Again, it is usually necessary to extend the meter probes. A favourite tool of the auto electrician is a 20 foot long meter extension wire with a crocodile clip that connects to the battery negative. Then neg grounds can be tested anywhere in the vehicle - especially rear light clusters - which are just about as far away from the battery as can be.

This is hopefully a simple explanation for motorhome owners - there are lots of Youtubes that explain multimeter continuity testing in more detail.