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Diagnosing a faulty switch


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This is how I go about testing a switch after I've confirmed that it has power going to it but is still inoperable.

You need to disconnect the suspect switch from the circuit-post-20199-0-45201500-1452144555_thumb.jpg

Using a Multimeter set to the 2k ohm scale (other scales can be used also)as shown touch the black probe on one connector and the Red probe on the other connector to check for resistance across the switch.

With the switch in the off position you should have an open circuit and have a reading of infinity as indicated by the 1 on my multimeter-post-20199-0-04813300-1452144978_thumb.jpg

With the switch in the on position you should get a low reading as now the circuit has been complete and is a closed circuit-post-20199-0-92746700-1452145081_thumb.jpg

Say for instance with the switch in the on and off position you had a reading of infinity indicated by the 1,you would have an open circuit with no power to your accessory.

Say for instance you had a low reading in both the on and off position,the accessory would be powered up at all times as that would be a closed circuit without the means to power off due to a broken switch.

You can do the same test using the multimeter set to check for continuity using the continuity symbol as shown by the multimeter here.In this case if the switch is working when in the on position you'd here a audible alarm an have a reading and in the off position you should hear no alarm and have a reading of 1(infinity)post-20199-0-36309200-1452145587_thumb.jpg

As you can see a multimeter is a very handy tool to have for all sorts of electrical testing.

This switch when I opened it up had dirty contacts and after a good clean is as good as new.

I know there's guys here that have issues with basic diagnostics of issues with there boats and I'm certain it will help someone out in future if they can't get someone to look at it for them.


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  • 2 weeks later...

You can test the switch in circuit if you use the voltage setting. With the switch in the off position you should have 12 volts across the terminals. With the switch in the on position the reading should be close to 0 volts as you have removed the potential across the terminals. It is a quick indication of the switch health without the need to remove. You can also test as Fab1 said without full removal of the switch by removing just the negative terminal (not the positive as you don't want this floating loose ready to short out other stuff). Ric.

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Edited by Ric001
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