first off i would unplug the adapter and test for 12v at the factory plug (where the yellow wire plugs into), if you dont have 12v there then i would either jump a wire off from your cigarette lighter (with a fus inline of course) or attempt to trace the short farther into the harness (could be a mess?). if you do have 12v at the factory harness then change the setting on your dvom to ohms and check the resistance from the wire end of the adapter to the terminal end, your reading should go from 1.00 to 0.00. if it stays at 1.00 then your yellow wire in the adapter is broken or the terminal was not properly crimped onto the wire when it was assembled. hope this helps you out, i hate to see this simple install spriral into such a nightmare for you but i know youll get it figured out, especially if your previous radio worked fine. as for combining the red and yellow wires, if theyre all tied together then your radio is always going to have 12v constant power, whether the key is on or off because you are feeding the red wire constant power from the yellow wire (once you figure out the constant 12v problem) so you want to keep them separate. is your dome light still working? i thought i remembered reading that it stopped working after your radio started working, so im thinking check your fuse panel (looking in the hanes manual it shoes that there is one behind one of your dash panels) location #8 controls the dome light, cargo light, power mirrors, and the digital clock (this will be the constant power to the radio).