Why is this light constantly on when the truck is running?

Your trailer has an auto tire inflation system? I think Its telling you you have a leak its having a hard time keeping up with... or its confuser is messed up

 

It is autoinflate on the trailer. Check the system for leaks and have the tires checked for flats and leaks. There is a valve to turn the system off and the light will go out if the leak is in a line and not a tire usually right by the box where pressure can be adjusted

 

Stop somewhere level and quietish, turn truck off, leave air supplied to trailer, find your air leak... those inflation systems can keep up with a lot of air coming out of a tire but you still need to fix/replace the tire before it goes.

 

Bevause you went over a really uneven patch, the air bag leveling system may also be grumpy , can try dumping all air to trailer, air tractor all the way up then give the trailer air to see if a simple "turn it off and back on" essmtially makes the bags happier, but that should have nothing to do with the tire inflation system

 

Auto inflation light will typically not come on or go off in a few minutes after inflating tires in a properly operating system with no leaks. A small leak can take 10-15 minutes for it to go off. If it's permanently on, you have a pretty big leak in the system or a tire should try to find the leak ASAP.

If it's within the system, there's a valve you can turn to shut off the system. If it's a tire, well, keep it on til you get it taken care of.

Don't just ignore the light just because the tires are inflated. If it's as audible of an air leak as you made it seem, that light will be a tattle tale to DOT and the air leak will probably be a violation, wherever it's coming from.

 

If you swing by a Love's and are friendly and honest about being new, someone might help ya out and walk out with you and give you a quick diagnosis of where the leak is coming from

A fellow driver could probably help ya out as well

 

Piece of duct tape,,,