OK, long story as short and sweet as I can make it. Started off with a weird battery drain, jumping it off about once a week, then the battery was less than 10 volts, so i tried another battery, ( I might have accidently reversed the polarity) it would only crank but not start so that didn't work, so I reconditioned and charged the original battery, put it in and it started right up....problem is no lights ANYWHERE, all I have is horn and hazards. It also wont shift out of park. I was advised to replace the 120 alt amp cartridge fuse. done. still no lights anywhere and I've called myself checking the other 3 fuses that it "could be", to no avail. I'm in no position to "throw parts at it, and I'm at a loss, PLEASE HELP.

 

A reversed battery will kill not only the 120A alternator fuse but also some other fuses. You need to check those.

 

I have replaced every fuse, I now have door/courtesy lights, the "key in ignition" buzzer. Still no dash, and head/tail lights and still wont shift out of park. Any other suggestions? what do I do next?

 

I have replaced every fuse, I now have door/courtesy lights, the "key in ignition" buzzer. Still no dash, and head/tail lights and still wont shift out of park. Any other suggestions? what do I do next?

 

It is quite seldom but electronics circuits are sometimes damaged by the reversed connection.

 

Which ones? please.

 

It's hard to tell for me without analyzing the car myself using measuring tools such as an oscilloscope, a TDR, an ESR meter and others. Electrolytic capacitors are sometimes damaged by the low impedanced reverse voltage if applied long time and it is useful to use an ESR meter for the judgement.

 

I agree, but where to start? fuse boxes or ecm?

 

Using a TDR, I'd start to check related lines that supply the DC12V to the dash, head/tail lights and the shift control lines. It would be also useful to check the impedance of related lines comparing with a good working 93 LS400 for the reference.

 

Another important issue is that to check lines where fuses were blown. When you replaced every fuse, did you take a note which lines had blown fuses? Those lines are very important to check. Fuses need some mili-seconds to be blown. This simply means that the reversed voltage was applied some mili-seconds and this might kill some units.