Ugly Electrical Problem 1987 CV

I have a 1987 Crown Vic LX Two Door. Recently the battery went dead overnight. I assumed I'd left a light on, but no such luck. The battery tested bad at Advance, so they replaced it under warranty. Put the new
battery in and left the car for 2 days. Went to start it and no battery whatsoever.
Brought the battery in and charged it on my charger. Put it in and left it overnight. This morning, the battery was dead again.
Last night I looked the car over for any signs of a light being on. I even disconnected the trunk light since I couldn't see it to verify it was off.
Where do I begin? I seem to remember someone once saying that a bad alternator would cause that. I will tell you that when I tried jumping it and driving it to advance, the car quit after a mile or so as if the alternator wasn't charging.
Thanks,
CJB
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wrote:

Since Advance will test it for free, I'd start there. Beyond that, if you have a volt meter, check to see if you have a short between the low and high amp sides of the solenoid switch. I had an 84 T-Bird that bit me that way once. I also had an 81 Escort with a bad rear window defogger switch that liked to drain batteries.
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