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1996 Ls400 Blowing Variety Of Fuses --- Wiper, Ignition, Gauge, Ecu-B,


tradin1
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I recently came back from vacation, turned on the car and it refused to start. After further inspection, i realized all of these fuses blow either as i replace them, or when the ignition is turned to on. Each one depends on which way it's configured but it leads me to believe there is a common ground issue, or a short in the wiring where all of the lines merge for these fuses. I don't have a wiring diagram and need assistance with that. Or if anyone has any ideas as to what might be causing this, i would definitely appreciate any advice.

The fuses that blow are inside the car and outside. The ones inside the car consist of, ignition, gauge, and wiper.

The ones in the engine bay consist of, Radio NO1, ECU-B, DOME-FR, and antenna.

Thanks

-R

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Welcome, Raza.

It is unusual that multiple fuses would blow like this. I would pull one of the fuses that blows and wire a 12v bulb, like a tail light or brake light bulb across the open fuse and plug it back in. Then watch the bulb and see if it glows. If it glows full bright, you have a dead short somewhere on the line. If it only glows partially bright, you have something less but still is a problem if that circuit is switched off.

Now, with the bulb in place and glowing, see if you can wiggle any wiring harness connected to the fuse box or that may be under the dash, near the firewall or near the fender well area. If the glow changes or stops altogether, you have isolated the short. I suspect that you may have a chafed harness somewhere that is shorting some wires to ground. I have heard of this happening on cars where the suspension has been lowered and the wheel rubs on the inner fender area (I believe it was the passenger side fender area).

Does your car have any modified suspension or wiring either by you or a previous owner?

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Welcome, Raza.

It is unusual that multiple fuses would blow like this. I would pull one of the fuses that blows and wire a 12v bulb, like a tail light or brake light bulb across the open fuse and plug it back in. Then watch the bulb and see if it glows. If it glows full bright, you have a dead short somewhere on the line. If it only glows partially bright, you have something less but still is a problem if that circuit is switched off.

Now, with the bulb in place and glowing, see if you can wiggle any wiring harness connected to the fuse box or that may be under the dash, near the firewall or near the fender well area. If the glow changes or stops altogether, you have isolated the short. I suspect that you may have a chafed harness somewhere that is shorting some wires to ground. I have heard of this happening on cars where the suspension has been lowered and the wheel rubs on the inner fender area (I believe it was the passenger side fender area).

Does your car have any modified suspension or wiring either by you or a previous owner?

I will try the bulb method for each of the fuses, the ECU-B fuse blows instantly so i know there is a short for sure. the car does not have to be on for it to blow. Any flow of current and that fuse blows.

The car does not have aftermarket suspension of any form.

Where does the wiring harness run from the ECU box? i see it goes into the wheel well area and then disappears.

Or an animal may have chewed the harness. How was it running before the trip?

I'm leaning towards this, trying to find areas where an animal may have gotten near the harness. Have not seen any visual indications of a rodent though.

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You may have to remove the right front tire and inner fender well plastic protector to see the harness. "Any current flow and the fuse blows" is not really true. It takes the rating of the fuse or higher current to get the fuse to blow. The bulb will allow current to flow while protecting the wiring...ie, it will not allow too much current to flow to prevent damage to the wiring. I think you are looking for a bright bulb glow and then start wiggling those wires in the harness leading away from the ECU. Remember some glow is normal but fully bright is a short. If you are not sure what that looks like, just hook the bulb directly across the battery and that will be fully lit.

The animal theory sounds plausible but I have usually found those to be opens rather than shorts. But would not yet rule it out.

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Ok we can rule out the animal theory, my brother in law says they were jumping the car and this fiasco happened.

I've pulled the fuse box in the engine compartment, some of the relay carriers look as if they had gotten hot at one point.

I was checking continuity on the ECU-B and i think it made it worse? It was have current flow before and now it seems to produce nothing. Does anyone have a wiring schematic of the setup?

Thanks

-R

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Uh-oh...so your brother in law says he jumped the car? What he is perhaps failing to tell you is that he accidentally reversed the polarity and got a big spark. Now, THAT kind of surge to the system will usually take out the 120 amp main fusible link. But yours seems to be ok, right? Maybe a harness is melted to the chassis? Hopefully, this is not the case.

Next step I would remove the ECU behind the glove box and see if the short circuits disappear. If it does disappear, your ECU may be the sole culprit but if not, then a harness may be toast. I do not have a schematic handy but you could get one from TIS for a small subscription fee.

See if you can get any more detail about what exactly happened during the jump. Did sparks fly? Do not tip your hand but sneak up on this 'theory' ^_^

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Uh-oh...so your brother in law says he jumped the car? What he is perhaps failing to tell you is that he accidentally reversed the polarity and got a big spark. Now, THAT kind of surge to the system will usually take out the 120 amp main fusible link. But yours seems to be ok, right? Maybe a harness is melted to the chassis? Hopefully, this is not the case.

Next step I would remove the ECU behind the glove box and see if the short circuits disappear. If it does disappear, your ECU may be the sole culprit but if not, then a harness may be toast. I do not have a schematic handy but you could get one from TIS for a small subscription fee.

See if you can get any more detail about what exactly happened during the jump. Did sparks fly? Do not tip your hand but sneak up on this 'theory' ^_^

I feel as if the ECU can't be the culprit because if it were the ecu, it would not have any impact on the dome light or the radio having a short as well. I think there's an issue with the harness somewhere and i need to find out where that issue is. When they jumped the car, nothing out of the ordinary was done. So no more info in that department. If the 120amp main fusible link was out, i wouldn't be blowing random fuses.

Thanks

-R

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I would have to lean toward the harness being chafed/burned somewhere and shorting to chassis, maybe close to the fuse box where it catches a bunch of circuits. I would still implement the light bulb tester and go around wiggling and jiggling connectors and harnesses around the fuse boxes while keeping an eye on the test light. Actually, I would find the simplest circuit there is that blows the fuse and trace that down. It wiill take some detective work but you can do it.

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I would have to lean toward the harness being chafed/burned somewhere and shorting to chassis, maybe close to the fuse box where it catches a bunch of circuits. I would still implement the light bulb tester and go around wiggling and jiggling connectors and harnesses around the fuse boxes while keeping an eye on the test light. Actually, I would find the simplest circuit there is that blows the fuse and trace that down. It wiill take some detective work but you can do it.

I was fiddling with the ECU-B fuse carrier yesterday, it had a ridiculous amount of current going through it. The wires accidentally touched, and now no life in that circuit...*BLEEP*...

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That's precisely why you use the test light...it limits the current for protection and gives you a visual. I would not even think of messing with that stuff without one.

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That's precisely why you use the test light...it limits the current for protection and gives you a visual. I would not even think of messing with that stuff without one.

well the fuses that were blowing now seem to not blow? they all have current running through them when i plug in a DMM. Really perplexed? the instrument cluster now turns on, but does not display any of the gauges outside the parking light. The Hvac does not work still, nor does the radio system...

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So the fuses have somehow stopped blowing for the time being, but i still have some very weird issues.

When i place the wiper fuse, the 20amp, the wipers refuse to turn off. The instrument cluster does not turn on, all i see is the P, seatbelt, and some other sign. Along with all that the dome lights do not work, and the car does not start, it does turn on though.

I individually checked all the relays in the engine bay today, and they all work just fine.

Any ideas guys? i'm still sort of blindly looking. The light bulb technique wont work now since nothing has a ridiculous amount of current running through it.

Thanks

-R

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So today i found an electrical schematic for the car, makes things much easier.

Started from the battery, worked to the ignition switch, to the fuse box inside the car. So far all of that has continuity and checks out to be doing what it's suppose to without any shorts. now that i know what each plug does, and each wire, i can unplug one at a time systematically while checking continuity to isolate whats going on. I think i might just be able to figure this out.

Thanks

-R

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It's good that you have found a schematic and can dig in a bit more. Keep thinking 'simple' however. Usually weird issues like this boil down to one rather simple issue, not a bunch of smaller things. It is easy to get "wrapped around the axle", if you know what I mean.

Because these issues began when your battery was jump started, I would look at the battery. Why did it need jumped in the first place? Is it really good?

Next, the ECU is highly suspect. And I am thinking it may have been damaged during the jump start. A voltage spike on the system is all it might take. A spike would stress components and take them out. It would also have stressed any aging capacitors that were on the 'edge' of failure and made them ineffective.

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Well all my dome lights and a few other things started working normally. But the cluster still doesnt turn on, no hvac, the lights inside don't turn on, and the car doesn't start.

The cause for the dome lights and a select other things was a bad door module on the driver side. now i need to figure out wtf is wrong with the rest of the car. This is really testing my patience now.

-R

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Correction

Radio has no music but speakers work, all the interior lights, exterior lights, light dimming, clock, hazards, rear lights, and a few other little things work. Still no Hvac so i'm going to start by isolating the Hvac module tomorrow. no cluster either but i see it slowly coming back to life.

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I do not see how things are "slowly coming back to life" but, IMO, it smacks of capacitor failure. "Dielectric healing" maybe?

So, your battery is known good and up to correct charge level, right?

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I do not see how things are "slowly coming back to life" but, IMO, it smacks of capacitor failure. "Dielectric healing" maybe?

So, your battery is known good and up to correct charge level, right?

Slowly coming to life because I'm isolating things and locating shorts. The seat ecu under the driver seat was causing a short. Pin b1 on the seat ecu was the issue, relaxed the ecu and now the radio, all interior lights, exterior lights, dimming, cluster headlight and high beam, hazards, and few others have come back because of that short.

Now I'm going to try and isolate the wipers turning on on their own. Before the b1 short they would run at the lowest speed instantly, they have since slowed down so the current has decreased through that circuit. If I had a current flow value diagram with the car off, I could check the flow in each fuse. But that's not an option for me at this point. I'm guessing another module is bad.

It was a bad MOV in the ecu seat module. Will post pics later.

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So i think everything electrical is toast.

I've replaced the body ecu, that fixed my wiper issue, replaced the seat ecu, that fixed my lights issue, replaced the hvac module which replaced my hvac system.

I manually tested the lights on the cluster, and it seems the ones that the "gauge" fuse supplies voltage to, that circuit is fried. So i'm going to need a new cluster at minimum, and then and ECU most likely since the car doesn't start.

How do i go about coding the ECU, and correcting the milage on the cluster?

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The MOV (Metal Oxide Varistor) is a surge protector that was probably doing it's job but it got overwhelmed and shorted out. Something really, really nasty likely happened during that jump start to take out so much of the electronics.

As far as setting the mileage in the cluster, I thought that was a dealer thing due to the sensitivity of mileage recalibration. Takes special software to re-flash.

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