I don't know about testing them but is is really easy to swap it out. MAKE SURE YOU CHANGE YOUR OIL PRESSURE SENDING UNIT!!! I would just pull it apart after switching the oil sending unit and plug the new one in to see if it works. Don't put the trim on and go for a drive.
This way it is easy to test the gauges and light bulbs. If there are any light bulbs out then just use ones from your original gauge cluster or go to the stealership, they are cheap. This is an easy job. 5 screws hold on the trim and then there are a few for the cluster itself. The hardest part was plugging in and disconnecting the electrical connector on the back; but doable.
If your trying to test it at the junkyard I cant help but most should have return policies and you can do all the testing in about 15min in the parking lot.
Idaho85
