98 deville major electrical problems

[foursixfan]

hi guys. im new to this forum. ive owned a few cadillacs, but never expierenced these problems. i have a 98 deville which i bought for 400 bucks. has 134k, im the second owner. put new battery in and car was fine. sat overnight and battery went dead. used a jump box, got it to run. now the prndl is flashing,only speedometer and odometer are working on the D.I.C. no radio,drivers seat(heated part works) windows work. but tried hooking up to obdii, and cant read the codes from pcm. also says may not start. but did the resistor bypass and that worked. car runs and drives sorta. tc and abs on, so only starts out in second gear. any help would be appreciated! would even send you money! thanks in advance

[KHE]

I would check the underhood & trunk fuse center contacts for corrosion and/or blown fuses. Was there any corrosion on the positive battery cable at the battery?

The battery draining overnight is caused by a parasitic load - you need to connect an ammeter in series with the negative battery cable and measure the current draw after the retained accecory power turns off (about 10 minutes). Remove and install fuses until you find the one that drops the current draw to a minimum. That procedure will isolate the problem to a specific circuit. Then you will need to use the wiring diagram to further isolate and locate the problem.