Simple logic circuit to light LED 1, or LED 2, or LED 3 based on NOR/AND input?

[LesCir]

I need to build an automobile  circuit that lights LED 1 if circuit A sends it 12v; lights LED 2 if circuit B sends it 12v; or lights LED 3 (and not LED 1 or LED 2)  if both circuits send it 12V.

I figured it out using three relays, but I'd much prefer a non-mechanical solution for reliability on the road and mounting space considerations.

Can someone give me some fairly specific pointers? I know nothing of IC's, except that I'm sure there are some that would help :-) I can read a schematic and solder on a breadboard but designing a circuit with anything beyond relays and diodes exceeds my skill level.  I need some hands-on examples of how to do it.

Thank,
s