On Thursday, February 16, 2017 at 9:54:18 AM UTC-6, Jonathan St. Cloud wrote:


Below is the key lock

http://www.tauntontrailers.co.uk/bra...lock-731-p.asp

Jon - That link is for the small lock with the 7mm diameter barrel. After some measuring I found that I needed the larger 9.5mm diameter lock which Taunton doesn't seem to carry.

I contacted AL-KO in Germany and they said I had a US made AL-KO coupler (2") so they couldn't help. I contacted US AL-KO and they gave me two AL-KO part numbers. The 7mm is 203216 and the 9.5mm is 203141. To determine what you need just measure the inside diameter of the round portion of the lock opening (I used the shanks of metric drill bits). I found what I needed on http://ebay.co.uk or just by googling the part number.

Here are some pictures of the coupler showing the keyhole and the two sizes of locks. http://derosaweb.net/aviation/asw27/.../AL-KO_Coupler

A couple of things to note;

1) At first the lock cylinder wouldn't insert all the way. I found that I had to file just a tiny bit of the sides of the small rectangular portion of the keyhole. There was something blocking the lock's full insertion which appears to have been left over from the manufacturing process.
2) The lock doesn't stay in place permanently. It is only inserted temporarily when being used and is completely removed afterwards.
3) At first I thought the lock wasn't working as the coupler handle could still be lifted. Looking inside the coupler I found that the lock works by preventing the retraction of the spring loaded component that captures the hitch ball. Now that I know this I might have been able to use a long shackle lock instead. Oh well.
4) Strange looking small keys so I took the keys to a local old school locksmith to get duplicates made. He ended up having to use a Ford automotive (!) key blank plus filing down the thickness to make it fit. $5 a key.

Best of luck. John OHM Ω