Either your airbag or the airbag controller is broken, or it has been broken, repaired and not reset.
There is a procedure in the workshop manual to reset the airbag module. Mine (2003) required a multistep procedure with switching the contact (key) swith on and off on specific intervals. There is an older procedure using the door contact switch.
The flash-pattern indicates what is wrong, see the workshop manual. There is a link somewhere on this forum.
You'll have to find the applicable version of the RS chapter yourself.
I'm not really sure a broken trailer(plug) can influence the airbaglight. It is not connected to the brakes or lighting or anything.