If we agree that 10G to the rear split to the 4 magnets gets the job done there here are a few different options to get it done:
NOTE: Updated chart - added color coding for different voltage $ loss.
New chart comments:
The 3, 5 and 20 percent values are ones that I just pulled out of a hat.
20 percent seems like a pretty high loss for something as important as brakes. I color coded it red because I really don't think they should have such a high loss.
3 percent seemed like a pretty good value for a critical circuit. My understanding is that this the value the boating community uses (abyc) for critical DC circuits.
The 5 percent value I just pulled out of no-where. If my trailer was already in the 5 percent or less range I might leave it unless there was a specific problem. If I had to redo it I would shoot for 3 percent or less.
Note that before this exercise I was going to run four 14 gauge wires to each wheel. Now I'm thinking that a redo should really shoot for the 3 percent or less value.
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NOTE: Distance is round trip - 25 feet hot side and 25 feet ground side.