'87 5KCSQ finally attacked by electrical gremlins:-(

[Kelvin]

I had a similar problem a little over a year ago. After driving for 
nearly four hours in heavy wet snow through the New York City area, one 
windshield wiper blade had come loose, so I stopped in a rest area on the 
side of the highway to fix it. I was leaning over an open trunk, 
retreiving a spare wiper blade from the spare tire well when I heard a 
tremendous noise rapidly approaching from the rear. I turned around to 
see a NY State DOT plow approaching at high speed and throwing water 
logged slush directly toward me. I managed to jump around to the 
passenger side of my car, a '92 100CSQ, but didn't manage to shut the 
trunk lid. I was still soaked, right through to my underwear, but the 
trunk was now filled with several gallons of stiff, salty slush. Within 
an hour I reached my motel for the night and managed to shovel out 90%+ 
of the slush (and change my own clothes). But three days late on my way 
home, I came out of a rest stop on the New Jersey Turnpike to find the 
car's alarm had gone off, the headlights were glowing dimly and an 
assortment of dash lights were glowing with varying intensities. I 
restarted the car with no difficulty and everything returned to normal, 
but when I turned off the engine when I got home all the symptoms 
reappeared. 

     To make a long story short, no pun intended, the salt water from the 
snow had collected in a well underneath my trunk floor on the driver's 
side of the car, which also happened to house a large cable connector 
(about 50 pins) for the factory installed wiring for the cell phone, 
which I didn't use. Since one or more leads in the harness of which that 
connector was a part are always live, the salt water shorted it out, 
producing all the symptoms. I had to dissassemble the connector, dry it 
out with a hair dryer before everything returned to normal. I then 
wrapped the connector in several plastic bags, tightly sealed with 
several rubber bands. I also disconnected the live wire in the harness at 
the battery. The problem will probably never recur, but, if it does, I 
won't have to spend eight hours trying to chase down the short circuit. 
I'd also love to kill the plow driver and would have, had I had a rifle 
in the car at the time he plowed me under the slush. 

     In any event, the problem you describe sounds exactly like a short 
circuit to ground somewhere. I'd look for where it's most likely to have 
been induced, like the new heater core you described.

Kelvin Kean