The first attempt was to run a small chain between the latches. The chain has problems when the locks are at the open position with swinging out of the way. It is important that the holes be the same place on both latches or the chains will bind. I tried hooking the chains into holes in the latches but that made the problem worse. The current solution is to use long screws to hold the chains in place clear of the screws. I need to add a short piece to keep the chain clear.

Assembly is easy. I drilled and tapped hole in the latch for some 10-32 screws. Choice of size had more to do with what was in my junk box than anything else. I used a jam nut and set the bolt as shown. I could just have easily drilled a clearance hole and put a nut on both side which is what was done on another version. The problem is making sure there is clearance for the nut to clear the lock body.

Once both sides were together and the tabs put back on the latches, I ran a length of chain between the screws. This picture shows the chain between both latches in the unlocked position.

Now we have both in the locked position. You cannot open the latch on the left because of the chain going to the lock on the right. Notice that the chain is tight in the open positions and loose in the locked position. I had tried several things and as a result did not get the holes in the exact same place on each tab. If I can get some replacements I will fix this.

This picture shows the lock on the right has been unlocked but the latch on the left can still hold the door closed.

When the lock side is locked, you cannot open the thumb latch. When the lock is open the thumb latch works as it should.