Installation advise for Air dump switch for 388 Peterbilt

This is similar to my question about the yellow wire http://www.thetruckersreport.com/tr...ed-trucking-forum/240862-the-yellow-wire.html.

First off, is your trailer equipped with a dump valve already? If so how is your trailer wired. The key is finding out what wire on the trailer connection controls the dump. In most cases you will need a duel pigtail set up.

If your tractor already has the second cable set up you might be able to put a switch on one of those wires and wire the dump valve to that on the trailer side. You need to some how disable your abs on that axle though when its dumped. (might be why tmc uses the yellow wire for abs) If you dont, the abs will go nuts trying to brake a wheels thats not firmly planted.

 

Id recommend putting the dump on the rear axle. Not the front. The whole idea of a dump valve on a spread is to get eight of that back axle so you can hit a dock, or tight parking spot. And for very tight turns. If you've got a big heavy load centered on that trailer, and you dump the front axle, the frame is just going to sag and put weight on those tires anyway. It's just too far off a bridge to gap with 45 thousand pounds. Put it on the back axle and it's only a ten foot over hang, much less stress on the frame.

 

I ve driven on trailers with front and others with rear dump. the frame doesnt sag enough to put weight on the front axle when dumped. Your talking about over 3 inches of suspension travel. I'd be worried if the trailer saged that much. That being said, your right, you do gain manuverability by dumping the rear. Either will reduce tire wear around turns.

 

It's really easy to test this. Next time you have a heavy load on the center of the trailer(coils are great for this) find a flat level spot and pull the rear axle up on 4x4's(one under each tire) dump the air on the trailer suspension(some dump when you set the breaks, others you will have to drain the tanks) now get out and look down that deck. The amount of sag will shock and probably scare you. Remember they put an arch in these trailers just to help combat that sag.

 

Is it connected to the center of the green or yellow pigtail? Is hot already? If its hot, all you need to do find the corresponding fuse in your fuse box. remove fuses one by one untill it goes "not hot" Put a switch on that wire.

If its not hot to start, its a bit harder. You need to find where that wire goes and add a fused circuit to make it hot. also need to add a switch.

You coudl use relays instead of switches, but if your fuse box is near where you want the switch, you could just put a switch inline.

 

Do you know if its the green or yellow pigtail that controls the dump?