Wondered what was happening -- I'm not entirely surprised with the resuts, but at least we're narrowing it down. I got my manual back and had a quick look last week, I'll study it again and get back to you tonight, but the timer module is now the most likely component.
In the meantime if you read this, and since you can do this at n/c, I would try substituting your Dad's timer module. Its mounted to the underside of the fuse panel, no need to flip the panel down. Many contacts on it and plastic clips so you sometimes have to use small screwdriver to gently pry it out.
The internal circuitry of this module is not shown in the manual, however it performs a variety of functions, some of which we've checked.
