Wiring for air dump on spread axle.

Wouldn't there be a standard position on the power connector for the dump, just like the other functions? This way you would use it with different trailers?

 

The small 4way plugs don't hold up very long. Plus if you want to run a pig tail cable they don't fit well. They make an auxiliary 7way that has a slightly different pattern so you can't plug them in wrong.
I've always run the standard 7way it's easy to get anther pigtail on the road if you need to. There is no standard way to wire the aux plug. My recommendation is if you run a ground in it to make sure it's the same as location as the primary. Just in case you have brain lapse and plug it in wrong it won't blow fuses.

 

I guess that's where I got confused.

That's how I did mine, like DL550CAT suggested. I have two 7-pin plugs on my tractor/trailer and I can switch either cable with either plug and everything functions the same.

 

We rarely unplug the cables on the logging trucks so that's good to know that they don't hold up over repeated plug/unplugging.