ABS light and codes on a 2002 Isuzu Rodeo

Having issues with tracking down a couple of troubles codes for my abs system.

1st code: 51 (FL Open or Shorted sensor)
2nd code: 53 (Rear Open or Shorted sensor)
3rd code: 61 (FL Missing sensor signal or signal dropout)
4th code: 63 (Rear missing sensor signal or sensor signal dropout)

I would assume 1 and 3 and 2 and 4 are related.

I cleaned the wiring harnesses for the Front Left sensor and the connector to the sensor itself and still nothing happened. The dealer said it was very rare to have a front abs sensor drop out (they didn't even have the part in stock). Baring spending over $300 dollars to replace a sensor that may or may not be bad. Anyone have any suggestions on what else I can try?

As far as the rear sensor. I followed this thread: http://www.automotiveforums.com/vbulletin/showthread.php?t=557922&highlight=abs+sensor

but there is no connector there. Just 4 wires (the bigger one coming from the front of the truck splits off to 3 others. One is trailer lights, two is the differential wire and three goes to somewhere over the gas tank.

I'm really at a stand still here so any help would be appreciated. Pictures are even better :)

Thanks in advance.
Jeff