I am in my second week of swapping a 289 from a 66 fairlane into my 67 mustang. All that is left is getting a short identified in the wiring ::. I have it narrowed down to two wires that come off the bigger post on the side of the starter relay that the battery cable attaches to. One is the yellow wire and black with yellow stripe wire that goes at some point to the regulator. The other one is a solid red wire that I can not find listed in my 67 schematic. The only red wire I can find listed in that location goes to the ammeter in a 66 schematic. My car was built in Nov of 66, so would it have still used a 66 model year wiring harness? I don't know if it will help me but I am grasping for anything at this point. Whenever I touch either of those wires to the post they are supposed to be attached to with the key turned on, the battery drains immediately and the regulator makes a clunking sound as sparks fly from the post. I have replaced the starter relay, had the starter and alternator checked, and replaced the alternator harness and starter wire. I have also traced the wires through the front of the radiator to the regulator looking for a crimp or open wire. If the red wire is to the ammeter for the 66 schematic, then I may pull the instrument panel and look for a problem there. Any electrical experts would be welcome to weigh in!
looking for short - need help identifying a wire
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The post on the starter relay is the main point that power feeds to the rest of the car's harness. Theoretically, both those wires are attached to every other power line in the car. What this means, unfortunately, is that _any_ power line in your car could be grounded. 
I hadn't thought of that because I just replaced it last year. I did take the cover off and it looked very clean and the points looked good. I will go ahead and have it tested though because it seems to be acting strange when ever I complete the circuit. The other thing that is nagging at the back of my mind is that when the engine was pulled I blasted some of the frame with aluminum oxide. I have noticed it got into some open places in the harness whereever the tape was removed. I am wondering if the aluminum oxide has made a coating on some connector somewhere and is causing the short. Not that it would be something I could ever fix, but I am wondering.
The new voltage regulator in my son's '65 lasted about 6 months ... then would drain the battery in about 2 hours. An easy way to tell is to remove a battery cable. Put an amp meter between the post and the cable and look at the amp draw. Then unplug the regulator and see if the amp draw drops to (or near) 0.
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