Trailer ABS light on. What to look for?

Hmm, I’d say no.
Being new, it’s entirely possible that the wheel bearings are loose.
Seeing as its weather related, I would think that a weather tight connector isn’t doing its job right. I found a corroded connection on mine last month, water got into the water tight connector joining a wheel sensor to an extension cable going to the ABS controller.

 

If light went on and then off. Like it fixed itself, while braking or driving through potholed parking lot.Prbably normal. But if it came on while running down the road, probably a bad wire or sensor, could be loose wheel bearing as mentioned.If you can do a blink test next time it’s on, you can narrow it down to which wheel is affected. Usually cycling the key 2 or 3 times then leaning it in on position and count the blinks. Find out procedure for your Truck/ Trailer, Otherwise Truckstop or dealer can check stored codes

 

I wanted to add, mine had a bad cable also same as Uncleal13. I changed sensor first on both wheels. $50 ea. Then figured out it was cable. Changed both cables from ecu to sensor cable ends. Kept old good 1 for future diagnosis $32 ea. Last week new one got damaged and put old one back on, Lol. Note which valve you have and which way it’s facing front or rear to get proper codes for either side. Otherwise like me you’ll read it as wrong side wheel. wcoastent.com has valve configurations and blink codes. It’s really not very complicated, once you read through how it works. I’d go for easiest cable replacement first, or try pushing sensors in against ring being careful not to damage wiring.