LED Toggle Switch Confusion

craigg

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Hello Everybody,

I apologize for jumping in here with what may be a simple minded question but I can't seem to figure out what's going on with a toggle switch that I'm installing to control a transmission cooler on my truck. Here is a picture of my switch and how it's wired (per instructions):
led_switch.jpg

The "Load" in this circuit is an electric fan in the transmission cooler. When I wire this switch as indicated to a D.C. power supply with a small incandescent bulb as the load the LED indicator on the switch lights normally. When I wire it in the truck with the trans cooler on the load terminal the switch works fine but the LED indicator will not light.

Question: Could it be that the LED side of the switch won't work because of the higher load of the fan? I don't know what the fan is drawing but it's probably in the 10a-15a range. The switch is rated 20a.

About the only thing I think i understand about these LED indicator switches is that there is some value of resistor in line with the light which is basically a diode. Sorry to be such a nube but please assume your talking to a LED 101 type of person here.

Thanks!
 

FRITZHID

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I've never had this issue with an LED switch but i'd suggest installing it in the truck and then using that incan bulb as a load, process of elimination style. if it lights with the bulb as a load but not the fan, then the fan is the issue, if it doesn't, then there's an issue farther up the circuit.
 

Lynx_Arc

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Without specs on the switch it is hard to tell what it going on. The switch itself should complete any circuit regardless of polarity when attached to the right 2 terminals and if you don't get the right polarities on the terminals the LED won't light at all because it needs + and - on the correct switch terminals to operate. LEDs are diodes and if the voltage flows one direction they will light (if correct voltage/current applied) but if the voltage is the wrong direction it won't light at all.
Essentially I can tell you have 1 + terminal and 1 - terminal but am unsure of the voltage of the load terminal itself if it is + or - or not. I'm guessing it may be a - load terminal and if you use the switch to complete a circuit to the + terminal of the battery etc you will have no - input to the LED for it to operate.
 
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DIWdiver

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I'm going to guess that the Batt+ and Load terminals are internally connected to a 20A toggle switch, and there's an LED and resistor between Load and GRN.

So if you install it and the fan goes on and off but the LED doesn't light, you have a bad GRN connection. This must be connected to the battery negative, which in almost all vehicles is ground. Your vehicle must be like this or the fan wouldn't come on when you connect the fan wire to Batt+ through this switch.

If that's not it, can you check the voltages on each pin, both when the fan is on and when it is off? That would help us diagnose your problem.
 

craigg

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If that's not it, can you check the voltages on each pin, both when the fan is on and when it is off? That would help us diagnose your problem.

Thank you all for the help. I connected the low wattage incandescent bulb as the load (i.e. middle terminal) in the truck and the LED lit with the switch as it should (so GRN is good?). I checked the amperage draw of the fan through the switch and measured 5.00 amps when running.

I will check voltages as suggested above and report the results. I'm just guessing but it seems as though the fan draws enough current that "what's left" can't pass through the resistor to light the LED? I realize that doesn't pass as an engineering assessment!
 
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craigg

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Results of voltage checks. Referring to the image and terminal labels above I measured these voltages with the trans cooler fan wired to center terminal:
Switch 'Off'
Batt + = 14.26v
Load = 0.00v
GRN = 0.00v

Switch 'On'
Batt + = 0.11v
Load = 0.07v
GRN = 0.00v

Results of voltage checks. Referring to the image and terminal labels above I measured these voltages with the incandescent bulb wired to center terminal:
Switch 'Off'
Batt + = 14.26v
Load = 0.00v
GRN = 0.00v

Switch 'On'
Batt + = 13.83v
Load = 13.83v
GRN = 0.10v

Sorry if too much data. Does it help? :thinking:

Thanks again.
 

Lynx_Arc

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Results of voltage checks. Referring to the image and terminal labels above I measured these voltages with the trans cooler fan wired to center terminal:
Switch 'Off'
Batt + = 14.26v
Load = 0.00v
GRN = 0.00v

Switch 'On'
Batt + = 0.11v
Load = 0.07v
GRN = 0.00v

Results of voltage checks. Referring to the image and terminal labels above I measured these voltages with the incandescent bulb wired to center terminal:
Switch 'Off'
Batt + = 14.26v
Load = 0.00v
GRN = 0.00v

Switch 'On'
Batt + = 13.83v
Load = 13.83v
GRN = 0.10v

Sorry if too much data. Does it help? :thinking:

Thanks again.

Across what point was your ground (black -) wire of your meter attached? and which wire did you use to test the 3 terminals (red/+ or black/-). Without a standard reference point it is hard to tell what is happening here but it appears that the switch connects power (batt +) to the load and the ground wire is only for powering the LED - side.
Unless the LED is burned up you could be able to get it to light up by connecting the battery + and ground terminals to the battery properly and turn the switch to ON. You don't need to connect the load to test LED itself.
 
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craigg

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Across what point was your ground (black -) wire of your meter attached?
In all cases I touched the voltmeter black lead to a chassis ground. A point that showed no significant resistance to the negative terminal on the battery. Correct? Incorrect?

and which wire did you use to test the 3 terminals (red/+ or black/-).
In all cases I used the voltmeter red lead to touch each of the switch terminals.

.....it appears that the switch connects power (batt +) to the load and the ground wire is only for powering the LED - side.
I believe this is correct.

Unless the LED is burned up you could be able to get it to light up by connecting the battery + and ground terminals to the battery properly and turn the switch to ON. You don't need to connect the load to test LED itself.
The LED does light up with the switch if I remove the fan (load) from the circuit. It does not light with the fan (i.e. 5.00 amps) but it does light with a small bulb as a load.
 

DIWdiver

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It sounds like you connected the meter correctly to make the measurements, but I don't see how those readings make sense. The 'switch on' readings with the fan connected say you pulled the battery voltage to 0.11V. I seriously doubt you did that.

That suggests that either you didn't make the measurement correctly, didn't report it correctly, or what you think is a Batt+ wire isn't.

I also don't believe that moving the fan wire from 0.0 to 0.07V caused the fan to run.
 

craigg

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Well,,, I am the third owner of this truck and the 2nd owner installed the trans cooler. Come to think of it, I really don't know how the switch controls the cooler fan, it just does. So it may be that what I'm taking as a direct feed from the battery is really in some kind of control circuit?

I may have to use the switch without the LED indicator. The switch works it's just easy to forget that the fan is on without an indicator.

I really appreciate everyone's help here. I learned a lot even though I couldn't resolve the issue.

Thanks!
 

Lynx_Arc

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Well,,, I am the third owner of this truck and the 2nd owner installed the trans cooler. Come to think of it, I really don't know how the switch controls the cooler fan, it just does. So it may be that what I'm taking as a direct feed from the battery is really in some kind of control circuit?

I may have to use the switch without the LED indicator. The switch works it's just easy to forget that the fan is on without an indicator.

I really appreciate everyone's help here. I learned a lot even though I couldn't resolve the issue.

Thanks!
I'm thinking the switch merely activates a relay that could be wired to connect the relay ground wire to ground that is how I would wire a switch.
 
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