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Thread: Ground Side Toggle Switch

  1. #1
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    Ground Side Toggle Switch

    Ok, I did the web research and cannot find a thing.

    I am running SPAL fans in my 55 Wagon. The ground goes to the temp sender and it also has a ground toggle in a supplemental switch panel under the dash. Flip the toggle and bypass the sender and the fan starts right up. Pretty basic ground side toggle right?

    So I want to run an indicator light to show the fan is on, so I bought some indicator lights from Ron Francis. Here's my question. Since the power is direct to the fan, can I run an alternate power lead to the indicator light at one side and wire the ground to the toggle? So the fan and indicator light are hot on one side from different sources and when I hit the toggle the fan comes on and the indicator lights up.

    Two power sources and one toggle at the ground to complete the circuit.

    This should not be an issue right? I am having a brain cramp.

    Thanks for the help boys and girls!

    Scorp

  2. #2
    Registered Member chevynut's Avatar
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    Is the "sender" just a switch that closes at a set temperature?

    If I understand what you're saying, you want to connect a light to come on anytime the fans are on. If so you are correct in assuming that you can use the same ground to turn the light on as you used to turn the fan on.

    By the way, are the sender and switch rated for the amps your fans draw? I would think you'd need a high current relay to switch the current. If you're using the standard dual SPAL fans, they draw 50 amps.
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  3. #3
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    Thanks CN-

    I wired the SPAL Fans using the stock Kwik Wire 12 circuit harness and then added a supplemental block to cover 3 more circuits. There is a fan relay incorporated into the fuse block with a hot feed to the fan. I will need to check the relay. The temp sender came with the SPAL set. I also have a SPAL wiring kit for the fans but figured it was a little cleaner using the prewired fan feed and relay from the harness. I will check the draw. I made the assumption that since it was pre-wired it was at the right amperage amount.

    Old rule- never assume

    The Toggle is a Pico 25 amp switch.

    So you dont see an issue with separate hot leads and a common ground? I didnt but just keep second guessing myself.

  4. #4
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    The feed to the fan has a relay at the fuse block with power fed to the fan via 14 gauge wire and it uses a 25 amp fuse at the fuse block. It also is a 14 circuit harness.

    Its a single fan. Sorry wasnt clear on that.
    Last edited by scorpion1110; 01-30-2020 at 06:01 PM.

  5. #5
    Registered Member chevynut's Avatar
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    There's no problem using separate power feeds....they all go back to the battery. Same with grounds.

    I'm curious how your circuit works. If the +12 terminal on your fan is connected to a relay, what activates the relay? You said the sensor was on the ground side of the fan. That doesn't make sense to me.

    What I THINK you have is the fan relay COIL connected to the sensor along with your toggle switch. The other side of the coil would go to +12V. The +12V power to the fan comes from the fuse, through the relay contacts, to the fan, and then to ground. That way makes sense to me. It doesn't make sense to have the sensor on the ground side of the fan motor which is what I thought you described. I might have just read it wrong since you didn't mention a relay at first.

    So if you connect a light to any +12V source and the ground on the light to the UNGROUNDED side of the toggle switch, in parallel with the sensor, it should work like you want it to.
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  6. #6
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    CN-

    I think I got this totally wrong.

    Heres is the schematic:

    Attachment 10463

    And here is the sender:

    Attachment 10464

    The wire going to the sender is a hot isnt it? The aluminum coupler has a ground and that completes the circuit when the motor gets to operating temp. When I brought the 14 gauge wire back from the sender to the toggle and then went to the ground from the other side, I am simply completing the circuit again. So the sender and toggle are powered, and when the car gets to operating temp the ground is completed. Hit the toggle and you just bypassed it.

    So my indicator light leads go to each side of the toggle. I only want it to come on when I throw the switch.

    However for any other toggle I put in (say for the prime fuel pump), I can power the indicator light and the accessory separately and common ground them through the toggle to light it up.

    I never thought to check the leads to see if they were hot, as I was just following the diagram.

    CN, do I have this right now?

    Scorp

  7. #7
    Registered Member chevynut's Avatar
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    The schematic shows just what I described above. Terminals 85 and 86 are the relay coil. I have no idea why they want you to use such large wires for the relay coil but it's not a problem. A 20 gauge or even smaller wire would work. Both the toggle switch and the sender can actuate the relay.

    The power coming in on common terminal 30 is the power that goes to the fan when the relay is actuated. #87 is the NO terminal.

    The wire going to the sender is technically "hot" (you would measure 12V on it with the ignition on) but it goes through the relay coil so all the sender does is make the circuit to ground. If the sender or toggle switch is closed, you would measure a ground at the #85 terminal. Any time you have an open circuit you would measure power all the way to the end of the circuit, until it's grounded. Technically 86 is the "hot" side of the relay coil. Hope that makes sense.

    You wouldn't want your light across the toggle switch because it would NOT light up when the switch is closed because you'd have ground on both sides of the toggle switch. In fact, it the light might ground the relay coil through the filament and make the fan run all the time.

    You want one side of the light connected to 12V and the other side to the relay coil side of the toggle switch, or to the sender terminal, or to the #85 terminal on the relay. It's all the same node electrically. That way, when either the toggle switch or the sender grounds the relay coil, it also grounds the light and turns it on.
    56 Nomad, Ramjet 502, Viper 6-speed T56, C4 Corvette front and rear suspension


    Other vehicles:

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    56 Chevy 210 4-door sedan
    57 Chevy 210 4-door sedan
    1962 327/340HP Corvette
    1961 Willys CJ3B Jeep
    2001 Porsche Boxster S
    2003 Chevy Silverado 2500 HD Duramax
    2019 GMC Sierra Denali Duramax

  8. #8
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    CN-

    Huge help as always. The funny thing is I initially intended to run 12V to the light and the other side to the relay coil side of the toggle, which would have worked. So I would have gotten it right but wouldnt have understood why.

    Not much on this when I was searching the web.

    Scorp

  9. #9
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    Resurrecting this thread due to my slow trip into insanity on this switch panel.

    I ran a supplemntal + feed to each indicator light at one side.
    I ran the other side of the light to one side of the toggle. One was Fuel pump and one fan.
    I ran the toggle to my ground box.

    So what happens when you flip the toggle switches?

    Fuel pump
    Ignition off. Flip toggle.Light comes on and pump activates. It does exactly what was expected and suggested by Laszlo. No problem there. Voltage measured at one side of toggle 12V. Flip switch, it grounds and no measurement. I think thats right.

    Electric fan
    Ignition off. Indicator faintly lit with toggle off. Measured volts and it reads about 9V. Hmm. Flip toggle and fan and light come on. Shut off toggle and fan stops but light still faintly lit. Hmmm again. Turn ignition to on and light goes out. Turn off igniton and light faintly lit. Hmmmm. Turn on wipers and light full on WTF?. OK lets check this out.
    Remove toggle. Ground light directly to car it lights up. Turn on ignition still lit. ok so its the toggle switch or wiriring. Replace toggle, re connect and same behavior.

    So what this is telling me is that the light is somehow finding ground through the toggle. I can not figure out how. Two switches and even reversed power feeds and the same thing happens. The light is faintly on with toggle off. Full off with ignition on and it comes on when wipers activated.

    Attached is a primitive schematic. Here are the hook-ups using the 14 circuit Kwik wire harness with a relayed fan hook up:

    1) 12v to fan and fan grounded
    2) trigger to sender which is grounded.
    3) bypass from sender to toggle which when activated grounds and turns on fan
    4) indicator light powered at one side from a separate source and common grounded at toggle one side.
    5) activate toggle and fan and light are on.

    When toggle is turned off, fan stops and light goes almost out. Ignition on kills light. Wiper on fully lights light. Fan unaffected by switches.

    Here is the schematic.

    Attachment 10472

    I am not an artist

    Any ideas?

    S
    Last edited by scorpion1110; 02-08-2020 at 11:23 AM.

  10. #10
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    Continued troubleshooting. When I remove the fan ground from the toggle, the light behaves as it should. Full dark at off. No impact from wiper switch or ignition. So its the fan circuit somehow.

    One point. Cluster, radio and turn signal switch not hooked up yet, but dont see how that would impact.

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