2 pigtales?

Yup, many different reasons for this OP

My current tractor has 3, one for the old trailers, one for the new trailers, one for tarp, lol

 

I'll bet if you supply power to that one pin punched on the aux you'll find you have an electric dump valve on one axle or the other. That's the way all our Transcraft & Fontaine trailers are.

 

Well like I say, may or may not be the case but we have a bunch of Fontaine steps with the sliding rear axle and every one of them with the extra 7-way has a dump valve wired to the pin that's punched. Now the plug may be something they put on every trailer and only add the dump if a customer orders it (look at all the extra wiring behind the dash, they have every wire for every option ever dreamed of but only use the ones you paid for).

 

I'd say with the original owner it powered a lift gate on the van trailer. They are most commonly used for power of lift axles or electric dump valves as most have already pointed out. @Hurst it's all already there sounds like you just need to hook it up and start saving on some tire wear with the rear electric dump valve. That's how my Fontaine is hooked up. Make sure if you do this there is a light on the switch in the cab or something to warn you if you forget to inflate the bags again.

 

Let me know if you figure it out. my trailer is a '12 Fontaine 53' step and has the same aux plug. Always wondered what it was for. I'm gonna put power to the punched pin and see what it does tomorrow

 

Look above the rear axle. If you have a dump valve there will be a bracket with a solenoid bolted to it. The solenoid will normally have a 90 degree fitting on it with a short piece of hose pointed down. The hose is the exhaust for the solenoid. The fitting and hose keeps road grime from getting in the solenoid.

 

Thanks. Never been under a trailer that had one. Sure would be nice to have though.

 

And that just inspired me to leave my nice warm bunk and go lay under the trailer to look. I didn't see a solenoid so I guess there isn't one. So maybe fontaine just puts the second plug on all trailers.