Tach is intermittent &other questions

[LongHauler]

Hi There,

I'm trying to tidy up a few things on my new to me 1982 300TD Wagon. First off the tach is intermittent. I've read that it's an easy fix but where is the pickup and what should i be looking for to get it running again? Also what is the vacuum box that is smack dab on top of the valve cover do? It has 3 lines running to it and 2 of mine were disconnected. Also when I was checking the spare tire there is what looks like an air hose wired into that area. Does this wagon have a remote spare tire air supply hose and if so where is the compressor?

Thanks