If the chain is broken, there is often just enough chain to get a hold of with a pair of needlenose pliers. Gently pull and hold the chain out. Wrap a twist-tie on the chain, so that you can at least advance the switches positions for testing. If the chain is broken and it is impossible to get to the end of it, or the switch has jammed up, or it is free-spinning, otherwise impossible to advance the positions, the switch can be dismantled and examined. See Destructive Identification
| Pos1 | Pos2 | Pos3 | Pos4 | |
|---|---|---|---|---|
| Top | _ | _ | _ | _ |
| Bot | _ | _ | _ | _ |
Since the most common pull chain switches are four-position, the following will reflect a four-position switch. Make a small chart with columns marked Pos1, Pos2, Pos3 and Pos4. If your switch has two layers with ports, make rows marked Top and Bot. The Top will be the layer with the markings. The Bottom will be the layer nearest the pull chain layer.
Straighten out one end of four paperclips. Insert these ends into the four ports in one layer of the switch. Springclips designed to hold the wires will hold them in place.
Now use the tester to check continuity between L + 1, L + 2, L + 3, 1 + 2, 2 + 3, and 1 + 3. Write down every connection in Pos1. If there is more than one connection in a position, write down all connections together (i.e. L+1, L+2 are positive, write down L+1+2)
Now pull the chain to advance the switch position. Again test all ports as above.
Again pull the chain to advance position and test all ports.
Pull the chain again to advance to position 4 and test all of the ports.
Now pull the chain again to advance to Pos1 again. Verify the connections first noted to be sure the switch has rotated all the way around.
Now if you have a second layer with ports move the paperclips to that layer and repeat the above steps.
You should have something like this...
| Pos1 | Pos2 | Pos3 | Pos4 | |
|---|---|---|---|---|
| Top | L+2 | L+3 | 0 | L+1 |
| Bot | L+2+3 | L+1+3 | L+1+2 | 1+2+3 |
When looking for a replacement switch it is best for comparison to have the Off position on either end of the chart. Sometimes a "natural off" can be easily seen, as above in Pos3, the Top layer has no connections. If we move that to one end, we get...
| Pos1 | Pos2 | Pos3 | Pos4 | |
|---|---|---|---|---|
| Top | 0 | L+1 | L+2 | L+3 |
| Bot | L+1+2 | 1+2+3 | L+2+3 | L+1+3 |
Often there is no 'natural off', and indeed sometimes any position can be used as Off. Check your notes on the wire positions; Black carries power into the switch. The position when there is no connection involving the port where the Black wire(s) belongs, is the Off position.
That's all there is to testing a pull chain switch. With the internal shunting written down, you should be able to locate a replacement switch that will work. If the numbering on your existing switch is out of numerical order, see link below.