why do most flatbed trailers have two electrical connectors?

I run two cords
A yellow and green. The green is the basic stuff and the yellow is basically extra power for the lift and dump axles and one trailer has extra lights that fired when in reverse for backing

 

Adding a dump valve is very easy. At least on the axle that Doesn't have the leveling valve. I'd have to think a minute how to do it on the axle with leveling valve.
But on the non leveling valve axle basically the dump valve just goes in line. Stops incoming air and dumps whats in the bags

 

I'm interested to add air dump valve and was wondering if there any reason why not to do manual push/pull valve on the trailer itself instead of electronic switch from the cab. I don't really want to do additional wiring in the cab and don't mind getting out when it's needed in those rare occasions.

 

Turning on a busy city street and your going to stop & get out to dump the air. You'll get tired of that really quickly.

 

Everybody behind you will too lol

 

Wireless switches are available .

 

I have mine wired to the truck
I believe it’s just a hot to the extra yellow cord I run and that goes to a junction box about 1/2 way back on my trailer then to the valve

It also has a small manual T type valve that when opened it dumps which will work on any truck not wired up like mine but wiring it up is pretty simple and you’ll like it once it’s done

 

That makes sense.

 

I was thinking of this too and was looking to get 12v wireless switch on Amazon. But then figured what if there is another person use same remote control while I'm doing 70+ mph on interstate.

 

I added a dump valve on the rear axle so it pivots on the front axle when used. My second receptacle is only
a four prong and only two of those prongs are being used. Positive to the dump valve and negative back to
the the tractor (nothing should be grounded to the trailer because the greased fifth wheel will sometimes
break electrical contact to the tractor).
.