trailer question

[qb12]

I purchased a used 02 outback (66 hrs). Love the boat and it looks great. Need to get photo posted here soon.

However, on the top front of the boatmate trailer there is what looks like a silver dollar size (something missing). I noticed by looking at some your photos posed there is like a black cap. Question, Am I doing any damage by the cap not being on there and what is it for.

[05mobiusxlv]

When I Picked up my new mobius, I noticed it was missing as well. I didn't ask what it was, just told them to order me one. And they just gave me a new steel cover that you could turn around, and it would keep your trailer brakes from locking when backing up, if you didnt have the right 5 prong light attachment.