I have 1998 LS 400.
While boosting the car due to the battery being dead. Accidentally connected the jumper cables crossed. Now the dash lights, Gage's, radio, tail lights, trunk opener etc does not work.
Have I damaged the computer or is there a fuse blown. Help

 

Likely a blown fuse, the manual should have a legend for the fuse boxes.

 

Open up the fuse box cover and look at the bank of fuses just beyond the main bunch, last row toward engine.

Look at the fuse which is 2nd from the left, 80A. Thats the one that blew when I did the same thing.

Now changing it is a bit of work compared to a normal smaller fuse.

You need to get access to a 8mm and 10mm socket. Smaller the ratchet the better.

Use the 10mm to undo the clamp and wire on the right side of the fuse block.
Lift it off. Now on the left side there is a slot that holds the "plastic base in place, lift it up. What you are doing is separating this fuse panel from the main section.

Now, you need to remove two bolts to get the old fuse out…the side closest to the engine uses a 10mm bolt/socket.

The one closest to the fuses takes a 8mm socket.

There is a flap/cover on each side..lift the flap to get to the bolt heads then remove the appropriate bolt (most likely 2nd from left)

Once out, (both sides) lift bas fuse and press in new.

Reverse to reassemble.

Auto part store had one up here in Ontario, so I would guess same down there.

If you have any questions ask away..

Oh, ..to be safe disconnect battery while doing the above to prevent blowing any others accidentally.

You will want to check the other "regular fuses" in particular fuse # 26 which is a 15A for the ETCS.

Hope this helps