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Discussion Starter #1
2019 F350 6.7- switches 5&6 (both 40a). I have the 5a fuse slide so that these switches will power on with the ignition off.

On #6 I am running two 12v relays, so very low draw. On #5 I am running a 25a DC-DC charger. This charger charges a battery in the bed, that is the battery that powers the relays when they are activated. (the #6 switch)

I tested this system several times and it worked fine for days. When I went to actually use it- no power on from either circuit. I don't know if it worked for a while, but when I went back to the bed 20 minutes after turning them on there was no power from either circuit. I was out of town so next morning I went to a local O'Reillys to borrow a multimeter to try to troubleshoot and it was all working again. Then I drove away and they both stopped working 5 minutes later.

Some other info that MIGHT be related:

This last time the #6 (low draw) was working for 10 minutes while I was parked; then when I started driving I turned on the #5 (higher draw) and when I checked 5 minutes later neither were working.

The lights come on in the switches to indicate they are turned on, both when working and when not working.

The dealer speculated that it was my wiring that was going in and out. Although this is possible, I highly doubt that BOTH circuits are working and then not working, then working again, then not, simultaneously. That's one in a million or worse odds.

Any ideas? The dealer says it is just straight fuses, so nothing that would trip and then automatically reset.

Thanks in advance.
 

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Solved... For anyone that might experience something similar, we found the problem. The issue was that we grounded to the bed of the truck, and then checked continuity to the bed. The power came from the upfitter switches, and that all works fine. The bed however, was not "grounded" well to the chassis, so there was no good ground. We had 'assumed' that the bed, being bolted to the frame, was grounded well. We ran a 6g ground wire from one of the grounds in the engine bay back to a ground bus in the bed and tied everything together; now everything works like a champ.
 
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