Trouble understanding aerator/bilge wiring

[@Reel_Chris]

I'm trying to add an aerator timer switch into a '19 Tracker Pro 170 that currently has a single switch that controls both the aerator and bilge pumps:
IMG_20220806_172057456.jpg

The back side of that panel looks like this:

IMG_20220806_172042319.jpgIMG_20220806_121212593.jpg

By process of elimination, i.e, removing the wires one at a time while the pump was running, these wires control the bilge pump and have nothing to do with the aerator:

IMG_20220806_172042319_4.jpg

Here's the part I don't understand - there are 13 volts across the two wires physically attached to the switch:

IMG_20220806_172042319_2.jpg

There are also 13 volts across the negative wire at the switch and the fuse wire, which I guess is obvious, because it's bridged from the switch wire:

IMG_20220806_172042319_3.jpg

What I don't understand is when the pump is turned on via the 3 position switch, the voltage remains 13 volts across both poles of the switch, but disappears between the two wires shown above. As a result, I can't figure out how to wire in the new switch, which requires voltage inputs and then an output to the pump.

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I tried using the double red wire coming off of the fuse as the output and the switch wires, which always have 12 volts as the inputs, and the voltage came through when the new switch was turned on, but it didn't run the pump.

Does anyone understand what's going on here? It's almost like the pump runs when the voltage is dropped to 0.

[MCPO]

Maybe this will help. It depends on where you are measuring the voltage. When a switch is off it is open and the voltage drop read across the switch is source voltage, in your case 13 volts. When a switch is on it is a short and the voltage read across a short is 0 volts.

[M-D]

JMO since I cannot put my meter on things...I do not believe there are any negative wires here, just positives being switched.
Negatives will be connected to the device being powered and run back to a negative bus somewhere.
My best guess is the power comes in on the fuse holder that has the two wires terminated under one spade connector, would be the wire that is not connected to the 2nd fuse holder.
IMO, you need a separate switch for the aerator and a separate switch for the bilge.
Figure out which fuse is for the aerator, disconnect it from the existing switch and extend/connect to a new switch that is rated higher (ampacity) than the aerator. Then come off the switch to the timer and from the timer to the aerator.

[@Reel_Chris]

The switch pictured above is both an on/off and a timer. It goes from off to on, 1 min off 1 on, 3 min off 1 on, 5 min off 1 on and 7 min off 1 on.

If I'm understanding the replies so far, the voltage across the existing switch is operating correctly. And, I was probably connecting things backwards when I was first trying to connect the new switch. I assumed it went power - switch - fuse - pump. But it's more likely power -> fuse -> switch -> pump. So, the wire I marked with black electrical tape in the picture above is the one that should be connected to the "out" blade on the timer switch. Does that sound right?

[McQuaig]

Chris, your switch is wired wrong. On these Carling switches the middle 2 terminals are the 12V (in) and the top and bottom ones are line(s) out. Here's a diagram. To add a timer to the aerator you would add it between the switch (aerator OUT wire) and the aerator itself.
SWITCH.jpg

[Bill Reynolds]

I think you are on the right track.
In marine wire color convention, a brown wire is for the bilge pump. On my boat, the livewell pump wire is brown with a white stripe but I don’t know if that is standard convention or mfg preference. If they are both the same color, it creates confusion when deciding which wire to hook to which pump.
There is not a ground circuit on the switch contacts, only positive 12 volts. The circuit goes to ground through the pump.

[Bill Reynolds]

Chris, your switch is wired wrong. On these Carling switches the middle 2 terminals are the 12V (in) and the top and bottom ones are line(s) out. Here's a diagram. To add a timer to the aerator you would add it between the switch (aerator OUT wire) and the aerator itself.
SWITCH.jpg

I think it will work as it is wired. It is a DPDT switch with the common lugs in the center. In one connection the positive wire is attached to the common and the pump wire is attached to the pole connector. It’s opposite on the other pole but should still work.

[Bradrodfish]

Chris, your switch is wired wrong. On these Carling switches the middle 2 terminals are the 12V (in) and the top and bottom ones are line(s) out. Here's a diagram. To add a timer to the aerator you would add it between the switch (aerator OUT wire) and the aerator itself.
SWITCH.jpg

Sir I believe it is wired correctly. This is how all tracker boats are wired.

Chris you can keep the switch you have to power up the Timer and just move the Brown wire to the aerator pump to the out of the timer. Add a power wire to the switch and run to the 12 volt to the aerator timer. Then last run a neg wire to the nearest ground hub or device that has a ground. Just find a location that the timer will fit and then drill the hole

[@Reel_Chris]

Brad, thanks for the specifics. I attached the brown wire to the timer out, the orange wire coming off the fuse to the positive terminal and ran a temporary wire direct from the negative terminal of the battery to the negative on the switch just for testing purposes:

temp wiring.jpg
That made the pump work perfectly. Trying to find a permanent negative to tap into in the rats nest of Tracker wiring was difficult. There were only a few, and most either went into a multi-wire junction, were twisted in a tight bundle with others or had no slack to work with. I briefly considered tapping off the negative wire into the cigarette lighter but that seemed like it would have too many amps running through it to be safe. So, I ended up splitting off the power wire into a console light that never gets used. It's not pretty, but works fine. Fitting the large switch took some modification of the plastic console and trimming of the sticker the switch came with but it turned out OK.

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Incidentally, does anyone know what the plastic collars around the other switch bodies are called? I'd like to get one for the new switch to make it uniform with the others.

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