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Discussion Starter #1
I've got a 2018 3500 HD D/A. Had an aux fuel tank installed a few months ago & it is currently set up for gravity drain. I have an electric solenoid shutoff valve (in addition to the manual isolation at the tank outlet) that i can control from the cab of the truck. I'm looking into adding a pump instead of relying on gravity drain alone. Can anyone guide me on where a good spot would be to tap into the truck wiring harness to power the pump and solenoid valve and switches? I'm looking for a power feed that is only hot when the ignition is on. My truck isn't equipped with any OEM auxiliary switches in the cab so I'll have to install one for the pump.
Thanks
 

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I've got a 2018 3500 HD D/A. Had an aux fuel tank installed a few months ago & it is currently set up for gravity drain. I have an electric solenoid shutoff valve (in addition to the manual isolation at the tank outlet) that i can control from the cab of the truck. I'm looking into adding a pump instead of relying on gravity drain alone. Can anyone guide me on where a good spot would be to tap into the truck wiring harness to power the pump and solenoid valve and switches? I'm looking for a power feed that is only hot when the ignition is on. My truck isn't equipped with any OEM auxiliary switches in the cab so I'll have to install one for the pump.
Thanks
Are you looking for a switched 12V supply that can actually power the pump with no additional relay required, or are you just looking for a place to connect the "signal" input to a relay/solenoid? I think the latter is a better option because I doubt there are any switched 12V circuits that you could tie into with sufficient excess current capacity to run your pump; you're better off just finding any switched 12V circuit and tapping into it to switch your relay/solenoid on and off and powering the relay/solenoid with a fused "home run" to the battery or alternator.

I know that doesn't answer your question, but clarifying that you are or are not looking for a circuit of any particular capacity will help others help you find what you need.
 

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Do you have an in the bed trailer connector? Some have used the trailer connector for power.
I believe the 12V aux power for the trailer is actually non-switched, meaning it's hot all the time.
 

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Discussion Starter #5
JD, thanks for the suggestion of a relay setup. I shoulda thought of doing that, but didn't so thanks for the reminder.

Mikey, we tow a 5th wheel RV and so the trailer harness is 'in use' when towing. It's during our towing trips I make most use of the aux tank so am leery of tapping into those circuits that may interfere with my trailer lights or brakes.

appreciate the input guys
 

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JD, thanks for the suggestion of a relay setup. I shoulda thought of doing that, but didn't so thanks for the reminder.

Mikey, we tow a 5th wheel RV and so the trailer harness is 'in use' when towing. It's during our towing trips I make most use of the aux tank so am leery of tapping into those circuits that may interfere with my trailer lights or brakes.

appreciate the input guys
The 12V AUX circuit isn't used for trailer lights or brakes (with the exception of some electric-over-hydraulic configurations), so that wouldn't be a problem. But it wouldn't solve your issue since it's not a switched circuit; it's constantly hot. Running your pump off that circuit could be a shortcut that would allow you to avoid a home-run to the battery, but I don't recommend this because if you're running any RV accessories off DC power (refrigerator would be the main concern while driving) then there's a good chance you'll exceed the 20A rating of that circuit and blow the fuse.

This thread may be of use: https://www.gm-trucks.com/forums/topic/205207-12-volt-power-sources-needed/

I would wire that switched 12V circuit to the switch terminal on the solenoid or relay. This will probably need a small fuse; look up the specs of the solenoid/relay to determine the size, but I bet 2.5A will be sufficient. You can use very small wire (probably 18 gauge or so) for this. Then you'll want to wire the supply side of the relay/solenoid to the battery/alternator with wire and a fuse to match the amp draw of your pump. Then your pump is connected directly to the solenoid/relay's switched output terminal.
 

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Discussion Starter #7
Great info JD, much appreciated. It'll be a few days before I can spend some time looking at the truck in detail to get a game plan together. Need to order the pump & stuff as well.
 

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I used a lighted toggle switch to run my aux tank fuel pump and NC solenoid. Put the switch out of the way on the side of the console. With the light it is clearly visible when on. I plugged it into the drivers side retained accessory power outlet.
 

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Discussion Starter #9 (Edited)
Thanks for the info 1Blue78. I think I saw your pics when doing searches on tank installs awhile back. By the time you posted I'd already gotten my pump and figured out the power source. Been putting things together over the last several days as I had time, but am finally done.

For the power source I used an 'add-a-tap' pigtail to the circuit for the heated steering wheel. The fuse for the circuit is in the driver side fuse panel.

Here are some pics of my setup. In all 3 I'm laying down under the drivers side of the truck looking up at the area where the truck bed meets the cab.
First photo shows the overall layout. The top of the pic is the bottom of the truck bed and the bright red section at the bottom of the pic is the rear of the cab. The inlet of the pump is the bottom most connection. The fuel line extends from the pump then curls up to the left where it goes thru a hole in the side of the truck bed and connects to the outlet fitting on the fuel tank in the bed of the truck. The top connection of the fuel pump is routed to the fitting on the OEM filler hose. I put that electrical sleeveing on the fuel lines to give them a little protection. I plan on mounting a plate on one of the bed cross-members to give added protection to the pump and lines from anything coming off the rear wheels when driving.

Next Photo to the right of the first is a pic of the pump (Facet model 40002 which has an internal suction filter and an anti-siphon valve). I bought the pump from Pegasus. The pump is mounted horizontally on one of the bed supports. The directions indicate the pump should be preferably mounted vertically, but it's not a requirement. Talked with a tech at Facet & he admitted that probably 90% of the pumps are mounted horizontally with no problem. You can see the pump is mounted towards one side of the bed support and that's to provide room for the end cap (silver cap at bottom of pump in this pic) and filter to be removed for service if needed. The 90 deg fitting I used from the pump I also bought from Pegasus. You can also see I ran a dedicated ground to where the pump mounts on the bed support. Something else on the pump I learned from talking with the tech is that if the pump is run 'dry' (i.e. the aux tank goes empty) that's ok for a couple of minutes, but longer will damage the pump. When I first turned on the pump it was pretty noisy, but quieted down as it started pumping fluid; had to prime I guess. After that I couldn't hear the pump when sitting in the driver seat with the truck running. Even hard to hear it when the truck isn't running....

Bottom Photo This pic is similar to the top pic, but shows a view that's a little bit higher up. The black bracket on the right side of the pic is a support that runs from the truck frame up to the bed.
 

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