Starting problem...Relay?

[Mitchell S. Haskins]

My 1988 Audi 90 Quattro has been experiencing some strange problems of late.
Seems that, if I drive it every day, it's fine, but when I let it sit more
than 24 hours without driving it, the Audi gods give me the curse of the
non-starting motor.  If I jump the batery, it starts just fine.  Any BTDT's
on this problem?  I'm fairly sure it's a relay, but, if it is, which one is
it?

TIA!

Mitchell S. Haskins
1988 Audi 90 Quattro