I'm looking build a larger wire wiring harness for 2 garmin graphs and the black box. Has anyone built their own wiring harness or purchased one? I can build one no problem. My question is, if you built your own, did you just cut the provided power cord and splice into that? If so, did you experience a voltage drop still? My thinking is if you ran 10ga, cut your provided power cord, stripped it back and spliced into it, say about a foot back from the connector, you wouldnt experience much of a voltage drop from the battery.

https://www.bassboatwired.com/products/bbw-graph-power-harness-kits

We can custom build you one to fit your needs!

I built my own. Ran 10ga wire from battery to the bow and soldered the number of ground wires and hot wires as needed for my electronic devices to the 10ga wire. It has been installed two years and I haven't experienced any voltage drop. I bought and would have preferred using a fuse block, but there just wasn't a good place to mount it after mounting live scope black box. Most people say not to use solder on boat connections because the vibrations will break the solder joints, but if my solder joints were good enough to last on Air Force aircraft, I think they will be ok on my boat.

The most important thing is to make sure you use marine grade wire.

And marine grade shrink tubing. It is some good stuff. Only shrink tubing I buy these days.