Blue wire on 7 Pin?

The ABS will operate off the brake lights if no constant power.

 

I ran belly dump a lot and we always used the blue wire for the dump control.They were older trailers though no abs.

 

Trailer ABS is supposed to receive constant power down the blue wire. Brake light power is just a failsafe backup. Will more than likely get harrassed by DOT if they inspected you and found out that the trailer ABS isn't functioning correctly.

What you'll likely need is a second electrical cord to run the trailer accessories. We just used to run a seperate 4 pin round connector for the trailer accessories on the units that required them.

 

Normal wiring
Green - right turn
Yellow - left turn
White - ground
Black - tail and running lights
Brown - clearance and side lights
Red - brake
Blue - abs
It may be worth throwing a box on your truck combine black and brown into black, aux switch to brown

on the nose of the trailer put a box converting the same, then use brown for aux

This assumes you have all leds or very minimal incandesent lamps though.

This is enough if all you need is a single switched power item. And is easy to put back to stock