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Old 01-01-2015, 05:13 PM   #1
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SPDT Switch Question

First off I am not a big fan of electrical work so sorry if this is a stupid easy question...I prefer mechanical work, lol.

Santa brought me some new light bars! But now I need to order several switches for them. The side and rear mounted light bars I want a switch by the corresponding doors, along with a switch on the dash for them. Looking online I need a SPDT switch so the lights can be controlled with either switch. Ok, I think I got that and it should work, right??

Second, the front light bar will only have the one dash mounted switch. Can I use a SPDT to control that, even though it will only be that single switch? I just want all my switches to match.

Thanks!!
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Old 01-01-2015, 06:57 PM   #2
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Re: SPDT Switch Question

YES, you can use a SPDT switch as a SPST switch. One of the end terminals will not be used when using as a SPST.
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Old 01-01-2015, 09:45 PM   #3
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Re: SPDT Switch Question

Quote:
Originally Posted by LeadDoggy
YES, you can use a SPDT switch as a SPST switch. One of the end terminals will not be used when using as a SPST.
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Old 01-02-2015, 12:26 AM   #4
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Re: SPDT Switch Question

Just make sure the switch can handle the load if you're operating several lights. Some of those big light bars may require a relay but should come with it. Check the specs. My 42" pulls about 20A
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Old 01-02-2015, 03:54 PM   #5
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Re: SPDT Switch Question

This may not be as easy as putting in a SPDT switch, you really need to know what the capacity of the circuit you are wiring into has, as now you could be asking it to provide power for both lights at the same time. Adding a relay would be the easiest way to attach to the existing circuit with minimal power draw. After that you need to understand if the current switch is switching the 12 Volt Power or a ground going to the other side of the light source. I would call one positive sourced and on negative sourced. I have attached some drawings of each, that should help explain, I did throw them together rather quickly so, if it doesn't make sense please ask, I may have screwed them up. In both cases the existing switch is used to control a SPDT relay. The new light will be controlled by the Normally Open input of the relay (87). We use a standard SPST switch going to the Normally Closed input of the relay (87a) Note: this switch must be capable of handling the current load to the new light (even if it is negative sourced) . In both cases the existing circuit only has to take on the added current load of the relay coil instead of the new light also.





hope this helps

-greg
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