you need a test light with an aligator clip and a probe...and ANYTHING could be the issue. circuit breakers can fail and so can wire. the circuit breaker could be fine but making poor contact. Using the test light you can look for actual power. I prefer the test light to a multimeter because you can see it more easily while you are probing wires, and also because it is possible to have a connection which reads as providing 12 volts on the meter but interupts when a greater load is applied. The light doesn't pull much juice, but it is is some, wheras the meter pulls almost no current.
Another test is to determine if the problem is on the ground or the positive side...you said you tested the motor, I'm guessing you attached another battery or another set of leads, but you should test both + and - seperately. Run a jumper from the wiper motor negative to the ground or battery negative and see if it works...if it does you had a bad ground. If not run a jumper from the battery positive to the wiper motor...if it works than the posive side of the circuit is the problem...it is unlikely that both + and - are both not connected, generally only one side fails...and the ground is more often the problem then the positive side (aside from blown fuses of couse).
Good Luck!!
Edit: It's a good idea to always use a fuse when you are connecting jumpers to various stuff for testing or diagnosic purposes...I learned this the "smoky" way.