Electric / Speedo question

[evill]

I just a 1977 911S on Friday from a friend.

I notice that when I shut the key to the off position, the speedo needle juumps from 0 to 30 and stays there. If I move the wiper stalk from off to an on position, with the key off, the needle drops to 0. When I turn the wiper switch off, the needle goes back to 30.

My friend says that if the car sits a few weeks, the battery dies, could this be the cause?

Any tips on what to check for this?

thanks,
Ed
A New 911 Owner