The switches I've seen have a specific direction they need to be installed in... they don't function well if the pin is 90* off... . I agree with the walk around test... but let me share why I carry a spare... BTW we were running commercial plates and DOT #'s... . I was in Canada, at a scale house and was going through a safety inspection... the inspector wanted to inspect the break away and pulled it out... he didn't pull it out straight and actually broke the plastic pin... thus locking the trailer brakes, and with a broken pin no way to move the trailer... You should have seen the look on the guys face as the broken piece dropped to the ground...
I said... . you broke it... I sure hope you have a replacement... he refused to offer a replacement and the argument moved to the office from the parking lot... Than an argument with the supervisor at the scale house started... he, finally conceded that they broke it and they started to call around and find a replacement for me... So the trailer is sitting there... with the brakes locked... drawing 10 amps of power. . to move the trailer out of the area I had to cut the wire to release the brakes... move and park the trailer... the closest one was 25 miles away. . I suggested they get in a pickup... and go get it... or have it delivered... under duress the supervisor called his boss and of course was scolded for not using the proper process to remove the pin... I finally drove the 25 miles. . the part in Canada was almost $10... .
When I got back to the shop. . I owned a business and we had several trailers. . I called our parts supplier and ordered a spare for every trailer... The interesting thing was that in the US we'd never had that break away system tested during the safety inspections...
I looked at some of our older trailers and this pin on them is aluminum but all I could find to purchase was plastic ones... so the lesson here is to have a spare and be careful. .