1997 850 GLT speedometer & trip computer problem

[stokoe7]

My 97 850 GLT has a trip computer that works sometimes and sometimes not (its always showing some sort of data that's correct sometimes and incorrect sometimes but not shutting off). Now the speedometer is starting to not move at all on occassion and the cruise control sometimes doesn't work too!! Sometimes they work and sometimes they don't. The battery is always getting corosion on the positive post and I thought that might be an indication that there is a short on the line but a mechanic says that's just the battery having a small leak and won't cause the problem.
Anu idea's on what is causing this on and off problem?
Thanks............ JOE[/b]