4 Wheel Drive/SUVs: battery, brake light switch, auto parts stores

Question
I hope you can help.

I have an 86 full size Bronco with a plow.  I bought a new battery for it, started it and it was fine.  The next day I go to start the Bronco and the battery is dead.  Thought it was a bad battery so I bought another.  It did the same thing.  What could be draining the battery?  It isn't anything left on such as lights.  It has to be in the engine or plow.

Thanks for your help,

Dan  

Answer
Dan,

Sometimes, a dirty, or bad switch can cause a drain such as this, but may not be quite enough of a drain to show on a light.  I have seen this happen with a stuck/bad brake light switch.  Sometimes a bad alternator can cause this to happen also.

If you do suspect the plow, disconnect it after charging the battery, and see if the battery still drains.  This would eliminate that.  Other than that, you might consider buying a repair manual, and trace out the wiring.

A  Chilton's or a Hayne's manual can be purchased at most auto parts stores for $20.  They have a lot of information on basic trouble shooting, and repairs, including a list of special tools that may be needed for a specific.  These manuals are designed for a year or range of years for specific vehicles, and are invaluable if you are planning on doing any repairs, or maintenance yourself.

Carl