Classic/Antique Car Repair: 73 Mustang battery drain, dick dick, auto literature

Question
Sir,
 Have a power drain on my 73 mustang with keys out.  Followed advise and pulled fuses until voltmeter dropped from 12v to 0v while hooked in series. Fuse was for court lamps/clock.  Disconnected them to no avail.  On a guess I pulled the (+) battery lead off the starter relay and pulled the other (+) wires off until drain stopped.  When I put the headlight lead back on the terminal the drain returned.  How should I continue tracking this down from where I'm currently at?  Any help would be appreciated.  Thanks.

Answer
You are going to need to get a wiring diagram for your car - if you already have a factory shop manual, that will be included. If you do not have one, get one from one of the auto literature dealers. I recommend Ed Faxon of www.faxonautolit.com, but there are others.

Once you have the wiring diagram, you'll have to follow it just as you would with a water leak in a complicated structure - namely, disconnect the main branches first until you locate the main branch that has the leakage (current drain in this case), then take each sub-lead from that main branch and disconnect them in turn until you find the one that is causing the drainage.  There is no easy way, this is just a painstaking detective job - I'm sorry that there is no quick solution.  In the meantime, disconnect the battery when the car is parked to keep from running the battery down.

From what you say, it appears the leakage is in the courtesy light circuit somewhere (it is powered through the headlight switch) but as for what exactly is staying on, I could not even guess.  Are you sure the glove box light, trunk light, or other interior light are not staying on?

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