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Help needed with passenger rear tail light blowing fuse

 
Old 03-22-2012, 02:32 AM
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napaul
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Default Help needed with passenger rear tail light blowing fuse

hello gents ! i seem to have a 7.5 amp fuse that is blowing as soon as i hit the turn signal for right hand turn. It is for the right rear turn signal lamp.I have checked the obvious of the tail light assembly and light socket. with tail light assembly unplugged it still pops right away.i believe i have a short somewhere in the blk/gr wire from central fuse box to the rear harness.
Does anybody know the path this harness takes from fuse box to rear of car.I can see it enters the engine bay but lose it when it ducks behind the airbox assembly. Where should i try looking for this short and how would some of you approach this check for continuity from fuse box to rear or section by section looking for a break in wire? It is confusing cause i do not know where these wires are hidden or path they travel when they enter the cabin anybody know?
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Old 03-22-2012, 02:35 AM
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i should also mention my front passenger side turn signal works fine only the right rear turn signal stop functioning as all other lights function properly in the right rear
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Old 03-22-2012, 03:34 AM
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I looked at the schematic and it shows that the 7.5 amp fuse is for the each side rear and side turn light only, not the front turn signal which is a different fuse. Do you have a side light?

The PET has a rudimentary drawing of the wiring of the car - from looking at it, it appears that the wire harness travels up the passenger side floor - there's probably someone who knows more about this harness.

Have you done anything recently around the fuse box....I'm thinking a possible source is the un-used and loose connection for the side light has gotten pinched, or possibly a screw driven into a frame member when re-installing trim...
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Old 03-22-2012, 10:48 AM
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No side light as it is an 89 c4. I was hoping somebody had a diagram showing the path this harness takes so I can look to see if wire is pinched or touching metal and going to ground when triggered by signal.
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Old 03-23-2012, 01:51 AM
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I think your best bet would be to pull the tail light assembly out and start checking the harness from there. I think that wiring is pretty close to the exhaust. On my car, the wire insulation burned completely off in spots and was shorting out. Hope that helps.
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Old 03-23-2012, 03:46 PM
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I would like to thank you I though their was just one fuse for the turn signals for the last three months my back right signal has not work I put new lights in on the right an left but the right side still did not work so I found out today my fuse # 33 was bad! now they work just like new.Thanks for your help. Vernon
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Old 03-24-2012, 10:54 AM
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Glad to hear it worked out!

I was blowing my #33 fuse as well, and blew it 4 times in a row.

Then I checked the taillight harness and it turned out that the smallest lightbulb (inside i believe) got corroded and was shorting out the wires for my turn signal. Not sure how or why the corroding caused it to short out the harness, but after cleaning, I tested for continuity and everything was fine. Put a new fuse in and never looked back.
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Old 03-24-2012, 07:20 PM
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well for me i know it's not the tail light assembly cause with it unplugged and removed if i put new fuse in and hit right turn signal front flashes and rear fuse 33 pops right away ran out of 7,5 amp so tried a 10 amp and pop goes the weasel. just have to start tracking down the short in the harness from fuse box to rear tail light.
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Old 03-28-2012, 12:50 AM
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alright guys can you help me make sense of this here is what i know so far. I removed fuse box after removing grund from battery. Looked underneath for chaffed wires or grounding point found none. Now if i put new fuse in with ignition off and hit the turn signal to the right the rear turn signal light stays on and doesn't pop fuse. If i turn on the ignition once i signal right fuse 33 for rear turn signal pops right away and all other lights function normal. Put new fuse in and if i hit my hazards it pops the fuse right away again. I thouight i found my culprit yesterday when i went under the passenger seat and there is a relay there with a blk/gr wire which i believe is for rear turn signal.Anyways removed relay to inspect and opened it up and i found middle pin was unslodered from circuit board so i resoldered and reinstalled with no change DAM! I know my lamp assembly is not at fault as fuse pops without it plugged in.
Does this sound like like the feed wire for that light is grounding out somewhere? i was able to trace harness into passenger front wheel well area but where does it go from there? does it run in behind the dash or underneath dash anywhere? would checking for continuity with meter show a short or grounding issue or do i need to check for resistance? Kinda hoping somebody with a better electrical understanding can point me in right direction.I know i could always run a new wire to rear tail light fro fuse box but i would prefer to find cause of issue.
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Old 03-28-2012, 09:20 AM
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Napaul,

Try emailing this gentleman, apparently he had a similar problem

https://rennlist.com/forums/7827974-post7.html

I'm thinking about some theories to explain what you,re seeing in your last post....
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Old 03-28-2012, 10:46 AM
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If I want to eliminate the signal stock on the steering colum and hazard switch as the cause could I try unplugging them one at a time and activating the right rear signal to see if 33 pops? I know how to unplug hazard switch how hard is it to get to the signal stock harness to unplug?
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Old 03-28-2012, 02:57 PM
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Those components are "upstream" of the fuse that's blowing, so they're not the problem.

What's significant is the fact that the fuse doesn't blow when the ignition switch isn't on, but blows when you turn the ignition to position #1, accessories on. That tells me you don't have a short to ground, but a short to a wire that goes to ground via a relay that energizes when the key is in position #1. I can't think of a relay that connects directly to ground - all the lights, etc. are connected to ground and their respective relays connect them to 12vdc.

What might be informative is to test the wire from the fuse to the light cluster when you turn the key. With the light cluster disconnected and the fuse removed, use a spade ( or crack open, and use 1/2 of a blown fuse) and insert it into one side of the fuse holder. Use your meter on volts with the "common" lead to a point of ground (bolt head, etc.), key removed, and cycle the turn signal switch and measure the voltage of the spade. Move the spade to the other side of the fuse, and do the same. What you should see is one side goes to 12vdc and the other remains at 0vdc. The side that goes to 12vdc is "upstream" of the fuse - the flasher, the hazard switch, and ultimately the + of the battery. You want to look at the other side. With the spade in the fuse holder, meter on volts connected to a good ground, measure the volts as you turn the key to position #1 and turn signal on. Do you get a reading? IF not, select resistance, and do the same thing. Do you get a low reading? If you got no readings, check your meter - hold the leads together in resistance mode and be sure you get zero. Test your battery, be sure you get over 12vdc. If you did get a reading, that wire is definitely shorted to another wire.

Hope this is clear.
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Old 03-29-2012, 01:04 AM
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ok here is what i can report after doing what mojorizing suggested. with tail lamp disconnected fuse removed if i put my meter comon ground on vehicle ground point in frunk and red lead to fire wall side of fuse holder and meter on voltage i only get 0.04 volts when i activate signal lever to right turn with no key. On the front side of the fuse holder towards bumper i get 0 volts with same procedure. Second part of your test is with meter to ground and red lead to front of fuse holder where i got no voltage if i insert the key activate the turn signal i still get no voltage but if i select resistance and do the same i get OFL reading. So what can i take away from this ? how do wires that were not shorting out before all of a sudden short out corrosion? since i haven't touched any wiring harness other than abs connector.
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Old 03-29-2012, 01:55 AM
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I got your PM.

The first test, with the key not turned, is to find out what side is the load (light) on the fuse. You should get 12vdc on one side of the fuse. Test your meter by testing the battery at the terminals, because you never got any voltage during this test. Tomorrow, I'll look at my car and we'll compare notes on what side of the fuse is what.

The second test, knowing now that you're on the downstream side of the fuse, is to turn the key to position #1 and observe voltage....if no voltage, switch to resistance and measure resistance to ground. If a hot wire or ground lead is shorted to your turn signal wire you'll find out. "OFL" is the reading you get when the probes or not touching each other, and you get 0 ohms when you bring them together.....thus testing your meter on resistance.
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Old 03-29-2012, 11:55 PM
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Maybe a small screw (or?) came loose somewhere and has lodged itself in the turn signal mechanism below steering wheel. I once had no brake lights, and came to find out that a small washer had found its way into the terminal(s) area of the small brake light sending unit in the pedal cluster, either shorting it or preventing any movement of the actuator. When crap like this happens, I always ask myself "what thing(s) were worked on or repaired-replaced lately, that could have led to this". I don't envy you this seeming labyrinthine quest for the problem! Sorry I'm no substantive help to you in your seemingly endless wire chase.
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