The most common and most likely answer to this crossword clue is the 6 letter word TOWBAR
I've seen this crossword clue in Financial Times
T
O
W
B
A
R
More clues leading to the result TOWBAR
Buddy explains!
The straight part
We know that "Connection with trailer" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case connection with trailer = towbar.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does TOWBAR mean?
TOWBAR noun- A bar, or ball, usually at the rear of a vehicle, where a trailer, or caravan or other similar item can be attached and towed.