I had the same problem. The former owner had wired a switch to kill the power on the trunk light fuse. The same fuse that powers that light, also powers the clock and the trip odometers when the ignition switch is off.
Stand on the left side, open the trunk and find the 10 amp fuse in the fuse holder on the right marked "Clock". Replace it if it is blown. If not, does it have about 12 volts on either side of the fuse? If not, release the fuse holder with a small screw driver, pull up the block and trace the power wire on the bottom of the fuse and see where you are losing power. You might find an add on switch like I did.