48 Cadillac wiring problem

[cadillac60]

I am far from an expert on wiring so I need some help.  I usually disconnect the battery when it sits overnight & have not had a problem.  I felt that I was going to use the car in the next few days so I left the battery hooked up this time. The battery is an Optima 6 volt & was completely dead. After a few days of slow charging it appears to be holding a charge. When I went to hook up the negative cable (ground) there was a good spark while I was putting the cable on the post. If my memory serves me right this indicates a short in the system?  If that is true how do I go about finding the short?

Bruce Watson

[Steve Passmore]

Could be a short but I think you would smell it. Could be something draining power, like maybe leaking down through your generator.  My son has an old Ford that has always done the same thing.  We make a point of fitting the battery breaker switches as the first thing we do to any car. I mount them on the floor below the drivers seat and knock it off whenever the car is parked up, the battery stays good all through the winter let alone overnight.

[35-709]

If your '48 has a trunk light or glove box light it could be staying on when it should not and that will be enough to drain the battery down overnight.  As Steve pointed out, it probably is not a short (unless that spark was really big) but more likely some kind of lesser drain on the system.  Electric clocks going bad will do it also.

[Glen]

If the battery has been disconnected for a while the clock will wind when you fist connect the battery and can cause a spark.  If you disconnect the battery and reconnect it before the clock winds down it wont case a spark the second time.   

You need to put an ammeter at the battery to see if there is a continuous drain or if it is intermittent like a clock. 

[Smedly]

I ran into this on my 46. I had a loose connection at the starter allowing the stud to turn in the solenoid. was not an issue until I moved the cable hooking and unhooking. maybe check this connection.
Sheldon Hay

[gary griffin]

Hi Bruce,

   Is it time to consider investing in a rewire job.  I have  had problems in the past with fire, shorts, dead battery's and so forth and it seems like a dog chasing his tail. Solve one problem and then a new one comes up. Our wiring was never intended to last  6 or 7 decades, and the varmints love to chew on them in hidden places.

   A good bit of work but to install a good new authentic wiring harness can be a good investment
in safety (Imagine losing your lights at night on a curvy mountain road), and reliability.

   They are not inexpensive but a good one will have correct looking, bundled and wrapped but new technology wiring harness with color codes per the manual.

   Peace of mind is not inexpensive though.

   

[cadillac60]

I appreciate all the input into the dead battery problem, after checking the trunk light, brake lights clock with no luck. I checked the heater control knob for the underseat heater there was the problem. the wires were very hot & I have to assume the switch ( I am sure an original has had it. Once I disconnected the wires to the heater & tried putting the Ground cable back on the battery there was no sign of any sparking.

Thanks again everyone.

Bruce Watson

[35-709]

   Bingo!  Good sleuthing.