120a Fuse Keeps Blowing

[Econ]

I hate to post up new problems, but I've searched and searched and can't find anything on this:

1991 LS 400 recently started having problems with the dash lights and radio blinking off (cutting out) when the brake was applied. Then, the battery died one very rainy day and the car has been sitting since.

I replaced the battery, but every time I connect the negative lead to the terminal on the battery, a huge spark jumps and the 120 amp main fuse (120A fusible link) blows.

I found the solution thread for the brake/dash light problem -- the possible worn wires in the left hinge of the trunk -- (here http://us.lexusownersclub.com/forums/index...c=17013&hl= for those of you who pull this up in a search) and inspected mine only to find three wires already patched with crimp connectors in place. I've replaced them with my own (they looked a little small for the wire) and inspected the rest of the wires, which looked fine.

Additionally, I had self-installed a CD changer in the trunk and had done a poor job of splicing on the ground wire (wht-blk striped wire) nearer the brake light. I repaired that connection as well.

I'm still stuck with the spark and then blowing fuse problem, however. I have checked for continuity between the positive and negative leads (while disconnected from the battery) and found that there was a completed circuit (~ 1450 kohms resistance, though). I wasn't sure if that indicative of a confirmed short somewhere or not.

My next step is to work on cleaning the ground points to ensure there aren't corrosion problems. Of course, I can connect the battery and the 30 amp fusible link to the starter and engine is fine. Anyone else have any suggestions as to where I should be looking?

Thanks for any help you all can provide. I appreciate it.

[SKperformance]

No other fuses in the system are blown?

Or else i would say pull all of them out and try running it.

You have multiple main fuse buses on the side of the fuse block in the engine bay ,disconnect then and try it.

[mehullica]

Is the battery a reverse post? Sounds like the battery terminals are being hooked up backwards due to the reverse post battery configuration.

[Econ]

SK - Good idea. Using that method, I should be able to narrow down which circuits might have a short, if it's a short at all.

Mehullica - Good catch as well - someone recommended that to me offline. I get a +12.5V when I test using where the neg and pos leads are currently hooked up - and -12.5V when I reverse it.

Thanks for the suggestions guys, I appreciate the quick feedback.

[maniek_LS]

SK - Good idea. Using that method, I should be able to narrow down which circuits might have a short, if it's a short at all.

Mehullica - Good catch as well - someone recommended that to me offline. I get a +12.5V when I test using where the neg and pos leads are currently hooked up - and -12.5V when I reverse it.

Thanks for the suggestions guys, I appreciate the quick feedback.

Econ,

I'll sugst you to open fuse box (near to 120A fuse) - as I remember called JB2 and unmoun board with fuses and relays and then check if there is no WATER inside. I had problems with my radio, A/C, trunk open by button and I went car to mechanic/electrician who opened this board (it is riveted and must be re-riveted) He found that all connectors were in water and made short circuits. After dry and applying special grese all works perfect !

Second check isolation on connectors for 120A fuse - there is large tube which can move up-down, maybe it was moved and un-isolated connectors (shorts to ground) ?

Regards,

Mariusz

[j.barleycorn]

Econ-

If all was well, then "something" changed and caused a short to ground. Best place to start is with what changed...

Did the dash lighting/radio issues start after you installed the CD changer? If so, perhaps the short is actually inside the changer itself (loose internal connection?), or part of the overall changer wiring?

[Econ]

Digging this out of the ground only to add a final solution.

Thanks to all that contributed ideas. Unfortunately, nothing can overcome the combined stupidity of Checker and I. Checker gave me a battery with the wrong polarity and I never had the good sense to actually check which side was the positive lead and which was the negative.

It did strike me as odd that the negative side of the battery would go straight to the junction box. <_<

Again, thanks to everyone. For those of you searching for a solution, check your battery terminals. On a 1st gen LS400, the positive post is on the left (standing at the front of the car) and the negative lead is on the right.