Chrysler Repair: electricial drain on battery, high beams, battery circuit

Question
I just recently purchased, 12/20/04, a 1990 New Yorker 5th Avenue with 59,000 miles with the only non-OEM accessory is a cd/am/fm unit installed just after the vehicle purchase.  In the past 48 hours, the battery has either been too weak to start, which required a jump or today it is totally dead.  I had both the battery and alternator analyzed yesterday and each are strong.  The alternator with no load is producing 14.3, while with high beams and fan on high producing 14.28 on average.

Battery, 2 years old 700CA, indicated strong as new.

I did not observe any lights or sounds while performing a walk around last evening and yet this morning the battery was too low for dome light to come on.

Weather is in the teens here, but have had colder weather and battery strong as ever until this weekend.

Any clues as to where to check?

Thanks,

Kyle Totten
Clarksburg WV

Answer
Hi Kyle,
The most direct way is to put an ammeter in the battery circuit (say by removing either clamp, probably the - post would be safer, then insert the meter between the clamp and the post) and measure the current that is being drawn. Then I would start pulling one fuse at a time (and replacing it promptly) but while each one is out see how that affects the current draw. Pulling one of those fuses will cause a sharp drop in current and that is the circuit that I would then start investigating to find out which component that draws thru the fuse is doing so inappropriately. Start in the power distribution center, then check the fuses in the cabin. The power distribution fuses generally feed the cabin fuses, so you will likely find 2 fuses that are the cause.  About the only circuit that isn't fused is the starter motor main power line. I have the '91 wiring diagrams but not the '90. But the chances are they will be similar, if your car has a power distribution center. So if you find the fuses that have an unusual level of current flowing let me know and I can suggest how to take it a step further and find out which component is doing the draw down of the battery.
Roland