Blowing a fuse when I turn on the headlights

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I have a '96 LX450...every time I turn on the headlights, the 15A Tail fuse keeps blowing and it knocks out my dashboard lights and my night time tail running lights. My turn signals and break lights still work, but the running lights are out.

Before I dive into trying to sort out the problem, I wanted to ask if there is anything I should look for (like its always a short HERE) or if there is any general advice before taking on an electrical problem.

I am armed with the following:

1. 1996 LC Electrical wiring diagram (cant find the 96 LX diagram)
2. soldering iron, wire, and flux
3. wire strippers, shrink wrap
4. motivation
5. understanding wife
6. Multi-meter
7. basic electrical understanding



would anyone have any advice?
 

ppc

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First thing I would look at is any trailer wiring harness. If that looks OK then I would unplug/disconnect the trailer light convertor box that most likely behind the inside right rear quarter trim panel. There is usually one wire that crosses from the right to left quarter panel underneath the chrome trim piece that holds the carpeting down that should be checked to make sure the insulation is intact.
 
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and my night time tail running lights.

That's the first thing I would suspect. Then the trailer harness. Then one of the tail/brake light assemblies, because they eventually degrade. One of mine lost its ground connection to the socket, which I fixed by soldering it. I suppose it's conceivable for one of the wires to come loose and short out.

The good news is that it happens every time, so it's not an intermittent short. I would disconnect the custom lights and trailer harness first, test it, and if it still blows fuses then just keep disconnecting sections while testing for continuity to ground until you find the problem.
 
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Same thing happened to me many years ago and I traced it down to the license plate light on my Slee 1st Gen Swingout tire carrier. The license plate light fixture had a sharp internal edge that over many years of opening and closing the swing out, allowed the single bulb wire to cut through the insulation and cause the tiniest of shorts. All it takes to draw 15+ amps and then most of the lights are out, exactly as you described.

At the time, I took one of the cyalume light sticks I keep in the back, snapped it for chemical light, and then laid it in the instrument cluster to light up the gauges for the (dark) drive home. When someone approached from behind, I'd occasionally tap the brake lights so they could see me...

I would suspect you have a similar short and would look at the wiring harness where they flex from opening and closing the rear tailgate and glass. Look for scuff marks on the harnesses and then test those circuits for errant ground continuity to find the short. Alternately, you can get to right area, go back at night - and with a new fuse in place - move the harness around and you may see the spark in the dark. Good luck,
 
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I feel like this may be the problem area because its exposed to mud and weather, looks to be a factory wiring that has been tied into and the problem I’m having is that my rear tail night time running lights are not working when the fuse is blown. It looks like this exact junction is where the EWD is showing a connection for those lights. Im not sure what all these wires are for in the pictures, but working through the EWD now. Also not sure what the loose green wire is for or if it should be grounded or if it fell out of one of these plugs. The wring going through the body to the tailgate looks good. The wiring behind the passenger tail light is also suspicious and will dive into that one next because its not as exposed and ”garage installed“ looking as what’s underneat.
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All these extra wires are the aftermarket rear camera tie in. The green wire end looks like it was twisted up with some other wire in this rat nest.

The wiring at the Spots where they go to the tailgate and the wiper motor all look to be ok

how do you go about checking conductivity at the fuse to the end in the back of the truck? My multi meter leads aren’t nearly that long. Do you make up a jumper wire?
 
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TomH

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I think you've found your problem, you just need to sort through it all.

There should be three stock connectors in that location that are used for a trailer harness. Some pictures here:

The long green wire is probably for a trailer harness and used to jump left/right side lights. I have a similar wire on my LX450 that runs under the carpet.

There is also a stock ground point at that location (BG) so not sure why somebody would add a ground point.

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It looks like the factory trailer harness has been bypassed and replaced with one up top…but I’m starting to think the short is upstream of the fuse because when I turn on the headlights, the TAIL fuse pops and the instrument panel and dash back lights go out. I’m not an electrical guy so this is all pretty foreign.

Is it possible that something in the Main 2.0L circuit from another fused circuit is causing the TAIL fuse to pop? I’m thinking this because when the tail fuse pops, the instrument cluster and dash back lights go out also
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It looks like the factory trailer harness has been bypassed and replaced with one up top
There isn't a *factory* trailer harness. They're all port or dealer-installed, and they're tucked in behind the right, rear body panel. I believe the one in your picture is original, but it's been awhile since I removed mine.
Is it possible that something in the Main 2.0L circuit from another fused circuit is causing the TAIL fuse to pop?
I don't see how.

Bypass that trailer harness. It's just inserted in the middle of the circuit. You unplug each end and plug those ends back together.

Disconnect that rat's nest underneath, too. My bet is on that being the problem.
 
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that yellow-and-black curly stuff is not OEM

disconnect the back-up camera from the main wiring, too, and repair the splices

(we are in Baton Rouge, too :cheers:)
:cheers:! I had to take a break from working on the truck, it with the humidity, Google said it felt like 104…but it felt way hotter than that!

Im about to get back at it and work on removing that rear camera, its pretty close to useless anyway. Ill replace it with a rear steel bumper!
 
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I finally got some time to mess with the rats nest of wiring and one of the ground wires came loose. Once I regrounded it (not sure if that’s a real word), all was good! All the lights work how they should now.
 

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