4Runner Blowing Fuse - REPOST

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  #1  
Old 09-08-03, 05:52 PM
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4Runner Blowing Fuse - REPOST

I tried to post this yesterday but they were making server changes and it would not show my message. Anyway here goes...

87 4Runner 4WD, w/22RE engine, EFI, 5speed. I've just had it repainted and since I have it back it blows the tail light fuse about 3 seconds after I turn on the headlights. The body shop removed the l & r tail light assembly and the l & r front assembly that comes on with the headlights. Everything appears to be fine with the assemblies and the wires and connectors when I looked them over.
I've tried to isolate the problem and I'll summarize what I've found. If I unplug & remove the front and rear assemblies that come on with the headlights it will still blow the fuse. That would mean all I have coming from the fuse panel under my dash to the rear is the wiring harness and the fuse still blows.

I noticed that below the fuse panel located under the dash on the drivers side was a good size pigtail that connected the wiring harness going to the rear to the fuse panel. I'm assuming this wiring harness contains both the left & right side tail lights although I don't know the right side wiring joins the harness if my assumption is correct.

Next, I unplugged that wiring harness from the fuse panel under the dash so all that is left is the fuse panel and the pigtail that connects to the rear wiring harness and now the fuse does NOT blow when I turn on the headlights. Reasoning that it does not blow the fuse when I isolate the rear wiring harness I'm assuming that somewhere I have something shorting out in the harness but if I have a short wouldn't that blow the fuse immediately instead the the 3 second period it takes? I'm using Buss ATC-15 fuses... are these delayed fuses maybe?

If it is a problem with the harness, any suggestions on isolating and fixing the problem wire?
Thanks
Dennis
 
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  #2  
Old 09-08-03, 07:32 PM
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the fuses are not delayed, but it does sound like you have a short to ground and that resistance to ground can vary causing the fuse to blow a few seconds later.
it can be hard to find a short to ground, but i would start by looking over any trim or anything that would have been removed during painting to see if the wiring somehow got pinched or a screw put through it causing it to short out.
you will need a good wiring diagram for that circuit and may want to get a subscription to all data there may be more than just your tail and park lights on that circuit often license plate lights and on some models dash lights are all controlled on the same circuit and any side marker lights if applicable, you will need to disconnect or atleast remove all bulbs to check resistance to ground to determine if harness is shorted out.
 
  #3  
Old 09-09-03, 03:25 AM
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idea

Do you have a trailor harness?I have seen quite a few that were causing problems.
 
  #4  
Old 09-09-03, 05:37 AM
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bejay,
I had checked what was removed and visibly looks okay, cannot find anything pinched, worn, damaged, etc. You are right about the license plate lights and tail gate window motor, I didn't think of that and also there is a rear cargo light that hasn't worked for years that I need to look at.

michael,
I do have a hitch on the 4Runner that was in place when I purchased is many years ago but had no wiring to connect a trailer but I crawled under and looked just to see if it did at one time but no dice, doesn't look like anything has ever been tied into the wiring back there.

Thanks for the ideas guys... I'll let you know something when I can get a little time today to check on it
 
  #5  
Old 09-09-03, 06:13 AM
Joe_F
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Start with the trailer harness. Most installations are very poorly done and are asking for problems later on.

The best trailer harnesses are ones that simply plug into the original harnesses with NO splicing.
 
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Old 09-10-03, 05:49 AM
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I didn't have time yesterday to do much but I did remove the bulbs from the license plate lights and unplugged the entire cargo light assembly and the fuse still blows when I turn on the light switch. These were the last items I'm aware of that were hooked to my rear wiring harness I had not removed. I do not have a trailer harness on this vehicle.

So far the only way I can get the fuse not to blow is to unplug the rear wiring harness from the fuse panel by the drivers left foot. When this is unplugged the fuse does NOT blow. I'm thinking this means my problem is located somewhere from the point where the wiring harness would plug into the fuse panel back. And because I've removed everything I know is hooked to the rear wiring harness and the fuse still blows when the harness is plugged into the fuse panel and does NOT blow when I unplug the wiring harness from the panel shouldn't that mean my problem is in the harness itself?

One other question... because the fuse does not blow when the rear wiring harness is unplugged from the fuse panel does this mean the switch is good because it is still in the live circuit???
 
  #7  
Old 09-10-03, 06:21 AM
Joe_F
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Sounds like a short in the harness. Get yourself a wiring diagram and look for any chaffing or rubbing of the harness/burned wires.
 
  #8  
Old 09-10-03, 08:13 AM
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sounds like a short

It sounds like you have a short in the back harness if you unplug it and all is good. You will need a schematic and a good multi meter and some time. I would start by visually checking the harness very carefully and slowly pulling it and looking at any points were it contacts the metal body. You might get lucky and find it chaffed and grounding out. Otherwise you will have to probe each wire and see with one is the problem. I wish you luck but I am pretty sure you can find it with some patience.You might need two people to do this one on the meter and one to jiggle the wires.
 
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