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Old 06-21-2018, 02:43 PM   #1
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12v Wiring Question - Help Needed!

I know positive to positive & negative to negative, but not much more than that. Any help is appreciated.


Goal:
I want to install a switched, thermostatically controlled, exhaust fan in the compartment behind my compressor fridge for ventilation and need to know how the wiring for all should go.

I want the switch to light up when "on" (not just when the fan is running due to the button thermostat kicking in at 100 degrees). What kind of wire do I need for the third contact on the lighted switch? Can I pig-tail from the other wiring needed here, or will I need a separate (pos or neg?) wire.


Equipment:
Here is a picture of the switch, fan, and button thermostat I have purchased for my project.
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Old 06-21-2018, 02:56 PM   #2
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Positive 12V wire into the back of the switch. Looks like you got a double throw switch ( 3 tabs on back) or may be a leg to power the light. One should say B and the other 1 or 2. 12V goes into the switch on the B terminal. You can use either leg as an out to the thermostat, just depends on if you want to rock the stitch up or down to turn it on. Red wire from back of switch to thermostat. Wire from other leg of thermostat to red wire on blower. Black wire on blower goes to 12V ground (negative). Hope this helps

I would put a small fuse inline between the 12v source you tap into on the trailer and the switch.
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Old 06-21-2018, 03:27 PM   #3
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Hi

A *lot* depends on just what that switch is set up to do. Assuming it *is* a 12V light on the switch ( and not 120V ) there will be a very specific way the three posts get hooked up. Some sort of data sheet should have come with the switch. If the bulb is 120V, you will need a different switch.

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Old 06-21-2018, 03:45 PM   #4
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Originally Posted by 68 TWind View Post
Positive 12V wire into the back of the switch. Looks like you got a double throw switch ( 3 tabs on back) or may be a leg to power the light. One should say B and the other 1 or 2. 12V goes into the switch on the B terminal. You can use either leg as an out to the thermostat, just depends on if you want to rock the stitch up or down to turn it on. Red wire from back of switch to thermostat. Wire from other leg of thermostat to red wire on blower. Black wire on blower goes to 12V ground (negative). Hope this helps

I would put a small fuse inline between the 12v source you tap into on the trailer and the switch.

Thanks. The switch is very poorly marked (very tiny & hard to read with a magnifying glass). Best I can make out is that it is marked 1a, 1b, & 2 if that makes any sense. One prong is silver colored, the other two are bronze colored.

Quote:
Originally Posted by uncle_bob View Post
Hi

A *lot* depends on just what that switch is set up to do. Assuming it *is* a 12V light on the switch ( and not 120V ) there will be a very specific way the three posts get hooked up. Some sort of data sheet should have come with the switch. If the bulb is 120V, you will need a different switch.

Bob

Thanks, but you'd be wrong (I wish you weren't). Unfortunately no instructions at all. But it is a 12v/10a lighted switch (I tested the light with a 12v source). Before ordering it, I noticed a complaint on Amazon for many switches like this was that they came with NO instructions whatsoever.
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Old 06-21-2018, 04:24 PM   #5
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Originally Posted by rowiebowie View Post
Thanks. The switch is very poorly marked (very tiny & hard to read with a magnifying glass). Best I can make out is that it is marked 1a, 1b, & 2 if that makes any sense. One prong is silver colored, the other two are bronze colored.




Thanks, but you'd be wrong (I wish you weren't). Unfortunately no instructions at all. But it is a 12v/10a lighted switch (I tested the light with a 12v source). Before ordering it, I noticed a complaint on Amazon for many switches like this was that they came with NO instructions whatsoever.
Hi

Well, if you already *know* what pins the LED is on, the rest should be pretty easy.

Bob
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Old 06-21-2018, 04:48 PM   #6
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I think it is a single pole, single throw switch.
One of the 3 terminals is for the common/ground for the negative side of the light (led).
The other 2 terminals are for the +12 volt side.
One is for the supply power of +12 volts.
The other is the switch leg.
The switch leg is tied into the indicator light internally.
I would use an ohm meter to check which 2 terminals read 0 ohms when the switch is on and infinity when the switch is off. I suspect the 2 silver terminals are where you will get continuity when the switch is on.
The gold terminal is common/ground for the light.
By connecting 12 volts to the switch you should be able to recognize which terminal is the switch leg because the light will be on regardless of the switch position.
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Old 06-21-2018, 05:06 PM   #7
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Hi

Well, if you already *know* what pins the LED is on, the rest should be pretty easy.

Bob

Bob, you give me too much credit. I tested using two-wire 12v source. Was able to get light to go on and able to get fan to turn on/off toggling the switch. One or the other, not both. How do I get light to go on & the fan? It seems I'll need a third wire.

Also, how do I wire in the button thermostat to control the fan? My first attempt powers the fan whether the switch is on or thermostat is on. Big fail. I need to divert some wires off the thermostat connections to withhold power to fan until thermostat clicks on and to go through the lighted switch first.
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Old 06-21-2018, 05:15 PM   #8
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Originally Posted by TG Twinkie View Post
I think it is a single pole, single throw switch.
One of the 3 terminals is for the common/ground for the negative side of the light (led).
The other 2 terminals are for the +12 volt side.
One is for the supply power of +12 volts.
The other is the switch leg.
The switch leg is tied into the indicator light internally.
I would use an ohm meter to check which 2 terminals read 0 ohms when the switch is on and infinity when the switch is off. I suspect the 2 silver terminals are where you will get continuity when the switch is on.
The gold terminal is common/ground for the light.
By connecting 12 volts to the switch you should be able to recognize which terminal is the switch leg because the light will be on regardless of the switch position.

Thanks, I will get my Harbor Freight tester out (never used it before) and trouble shoot.

Any tips on the circuit for the thermostat and fan? My goal is switch control first, thermostat second. All will be wired to the fuse panel such that it will be off when the battery switch is in "disconnected" position to prevent battery drain. It's only that last part I've got figured out.

Note: I had help lined up, but my neighbor couldn't do it last month due to his vacation. This month, before we could get together, he contracted Shingles. I got my shot last year; but like many others; he didn't know there was a vaccine. To hear him tell it, you should get you're shot if you are of a certain age. He's in a bad way.
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Old 06-21-2018, 07:10 PM   #9
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Quote:
Originally Posted by TG Twinkie View Post
I think it is a single pole, single throw switch.
One of the 3 terminals is for the common/ground for the negative side of the light (led).
The other 2 terminals are for the +12 volt side.
One is for the supply power of +12 volts.
The other is the switch leg.
The switch leg is tied into the indicator light internally.
I would use an ohm meter to check which 2 terminals read 0 ohms when the switch is on and infinity when the switch is off. I suspect the 2 silver terminals are where you will get continuity when the switch is on.
The gold terminal is common/ground for the light.
By connecting 12 volts to the switch you should be able to recognize which terminal is the switch leg because the light will be on regardless of the switch position.

Yes - this is how most illuminated switches work to turn on indicator light when turned on. I've installed several on my rig.
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Old 06-21-2018, 09:58 PM   #10
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Connect the black wire of the fan to common/ground.
Connect the red wire of the fan to one of the terminals on the thermostat. Connect the switch leg of the switch to the other terminal on the thermostat.
In other words, wire the thermostat in series with the switch and fan.
Keep in mind, when the temp is below the set point of the thermostat (100 degrees) and the switch is on. The fan won't run. Because it is not hot enough for the thermostat to close.
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Old 06-22-2018, 08:15 AM   #11
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Originally Posted by TG Twinkie View Post
Connect the black wire of the fan to common/ground.
Connect the red wire of the fan to one of the terminals on the thermostat. Connect the switch leg of the switch to the other terminal on the thermostat.
In other words, wire the thermostat in series with the switch and fan.
Keep in mind, when the temp is below the set point of the thermostat (100 degrees) and the switch is on. The fan won't run. Because it is not hot enough for the thermostat to close.

Thanks for making it clear and simple, which what I need. I should have set all this up on my work bench first, but I was in too much of a hurry to mount the fan behind the microwave which meant I didn't have the luxury to experiment without possibly screwing something up in the RV. Plus, it's very hot now and while working on this I have all the power off. Did I mention it's hot?


I chose the squirrel-cage fan because it is a small, efficient design, but most importantly because it requires only a 1-1/4" outlet port (important because I have very limited cabinet area to exhaust the air). I'll end up with a 16 CFM fan that turns on at 100degrees/off at 80 degrees only when both the lighted switch and battery connect switch are "on".


I'll post pictures when completed.
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