On the 79 non turbo there is a metal tube that angles out from the ALDA. It looks like a vac line should be attached to it. If you pull a vacuum on it with the engine running it will shut the engine off. I tried for some time to find the function of that but I have never been able to find anything.
Just forget about it. It is on all of those early diesels and never have seen anything usefull hooked up to it.