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Resolved blowing 10Amp tail-light fuse

Posted by sacrileger, Jul 15, 2019

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  1. sacrileger

    sacrileger Proven Member

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    Orillia, ON, Canada
    I have started blowing the 10Amp tail-light fuse for no apparent reason... the result is that my dash and instrument panel/cluster has no lights. The radio has power and lights work. The tail lights dont work.

    taillight.png
    taillight2.jpg
    taillight3.jpg
    taillight4.jpg

    From other posts on this forum, my understanding is that the dimmer switch in the instrument panel is often the problem. My dimmer switch is wired so that it is always ON and the dimming is not functional. One wire to the dimmer was cut and connected to some other wire so the dimmer is always in the max ON state/position. This was done many years ago when an aftermarket anti-theft system was installed on this car. Due to the after market anti-theft system, the car runs always and full-time with all lights ON, including tail and side marker lights. Before I start ripping the dash out and messing with the dimmer, what should i check for first to eliminate the obvious....? What could possibly fail in the schema to blow the 10Amp fuse?
    What is the likelyhood the anti-theft system is the problem here? I should add the anti-theft system does not work, i dont have the remote control for it and the wiring is very complex... it's somehow connected at the fuse box and the unit just hangs there.
     
    Last edited: Jul 15, 2019
  2. iugrad92turbo

    iugrad92turbo Proven Member

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    Check your grounds all of them, and look for wires that my be exposed with wiring a 25 year old car could be a simple solution, or a headache.
     

    2K  1

    1992 Eagle Talon TSi AWD
    awd · manual · 1G DSM

    6K  4

    1992 Eagle Talon TSi
    awd · manual · 1G DSM
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  3. Cherry

    Cherry Proven Member

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    Im guessing they wired into the lights so if the dome light came on the system would be triggered, and it might of flashed the lights. I remember you said you went through all the grounds before since you werent getting the right voltages to certain pins and cleaned them up. I would look for cracked wires which can cause problems. Like 92turbo said, the wiring on these cars are old.
     

    Street Build 225  3

    1991 Mitsubishi Eclipse N/T
    fwd · manual · 1G DSM
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  4. motomattx

    motomattx Proven Member

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    In my 2g it happened to be the sun visor with the built in vanity lights, I dont remember whether the 1g had those or not but if it does its something to check.
     

    Drag Race Build 2K  16

    1995 Mitsubishi Eclipse GST
    fwd · manual · 2G DSM
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  5. sacrileger

    sacrileger Proven Member

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    ok,.. so i did checked and cleaned up all ground wires. I followed this excellent post which lists all the grounds:
    Grounding Kit?

    However, that did not fix the problem.

    you mentioned exposed wires. well, i found a few places where wires were exposed under the dash. the previous owner installed an anti-theft, remote started, etc. unit in the car and the installer just kept cutting and splicing wires to connect the unit. many times wires were left exposed and not wrapped with el. tape. so i fixed that. needless to say, there were 23 splices i dealt with to yank the alarm system out. (see pic), i even ripped the dash out to examine the dimmer switch; however, the problem still persists and is not fixed. I am now trying to test the relay which is the next component between the battery and fuse box. I cannot find any good resource on how to test the tail-light relay... any ideas how to eliminate relay which is on the same circuit from consideration and the cause of the problem?
    photo 1.JPG
     
  6. sacrileger

    sacrileger Proven Member

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    photo 2.JPG
    i checked the grounds and that was not the problem. the interior lights appear to work fine too. i disconnected all tail lights and marker lights to narrow it down.. that did not do it. i ripped the instrument panel out to eliminate the dimmer switch. nothing. i am now trying to test the next thing on the circuit.. which is the relay but not having much success since i dont know how it's supposed to behave on it's own....
     
  7. sacrileger

    sacrileger Proven Member

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    the 1G does not have vanity lights.. just dome light and 2 lights under the dash. and the light in the trunk. all work fine and the problem is not eliminated if i disconnect all lights. at this point i am running out of ideas...
     
  8. Cherry

    Cherry Proven Member

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    I was just trying to figure out why they would wire an anti-theft system to the lights, but a lot of systems flash the lights and you need a way to trigger the system. The dome light comes on when the door is opened so when the system is armed when the dome light turns on it triggers the system. It might also flash the lights like most modern anti-theft systems.

    Is it just the tail lights that wont come on? Do the front parking lights work? If so you could technically run the tail lights off of that. At least you didnt lose all of your lights like I did and instead of trying to find the problem I just created a whole seperate harness for the lights basically. I would like to get it to work off of the stock switch but at least I have lights. My parking lights, tail lights, interior lights and side marker lights are all one circuit. I have a fuse box for it all and just ran slightly thicker wire than stock which the purpose of the relay is so you dont have to run a thicker gauge wire throughout the harness to cut down on the costs of wire.

    So lets say instead of running 10-12g wire throughout the car, they run 10-12g to the relays and thenthe rest will be like 16-18g which is cheaper. Then you have a switch that triggers the relay that completes that circuit which sends power to whatever you want to power. That is my understanding from my research at least and if someone corrects me then by all means take their word on it and we will both learn something LOL.
     

    Street Build 225  3

    1991 Mitsubishi Eclipse N/T
    fwd · manual · 1G DSM
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  9. sacrileger

    sacrileger Proven Member

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    Orillia, ON, Canada
    i tried to figure out how the anti-theft system that was installed on mine worked as i was disconnecting it.
    it appears that the system was triggered as soon as door was opened as the door switch right above the rocker panel was cut, tapped in and wire was run from there to the the harness at the front (see pics).. however, that does not appear to be the issue.
    photo 1.JPG
    photo 2.JPG
    also, the wire which feeds the tiny light bulb under the dash was tapped twice.
    photo 3.JPG

    so i dont know, this works as it supposed to.. including dome lights and fading as far as i can say irrespective of the hatchet job. perhaps this is a workaround to detect the passenger door was opened instead of the driver side door.

    what does not work are the the tail lights, the front side parking lights (orange) and the marker lights on the back quarter panels.

    i think i am quite close to finding the problem since i isolated the issue to the part of the harness under the dash and the tail light relay. if i can eliminate the relay being faulty then the problem is under the dash and i think i can find that since it is all in one place and the wires that were spliced i marked.

    There's just one more thing that puzzles me.. and i am not sure how that is wired... it's the switch which triggers a signal that the clutch pedal was pressed and the cranking can start. mine is disconnected and i can start the car without touching the clutch pedal. somehow the installers got around that issue.. which is a nice feature btw.

    nevertheless, there's a chance the relay is faulty as i am getting on/off power reading on different terminals depending on the position of the ignition key when the relay is disconnected so that part, the switching, is functional. on the other hand, i tried to put a different relay in the same spot and the lights did not come on...
     
  10. Cherry

    Cherry Proven Member

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    Well, I remember seeing one thread somewhere, i dont know if there was a gaining HP thread and things you should do first just from a maintenance standpoint like changing spark plugs, timing belt, spark plug wires and a few other things. I think one of them was to just unplug the clutch switch so you dont have to push the clutch in to start it which helps save something... thrust bearing maybe? Ill have to find the thread. The thread just says to disconnect it.

    But if you arent getting any parking light which is the orange front corners, tail lights and side markers then you just have to go through that circuit to find the fault. I think its a green wire with yellow stripe. If it isnt then I have no idea why that color combination is standing out to me.
     

    Street Build 225  3

    1991 Mitsubishi Eclipse N/T
    fwd · manual · 1G DSM
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  11. sacrileger

    sacrileger Proven Member

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    yes, ... i read the same thread. it was about saving thrust bearings in the winter when the oil takes time to get b/w the crankshaft and bearings.

    so, .. ya.. i just have to figure out how to test the relay and eliminate that component out of the circuit...once that is done, there's an extremely good chance the problem is under the dash where all the wires were spliced...
     
  12. Cherry

    Cherry Proven Member

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    I would swap it with another working relay that you know is good as long as the part numbers match. I think the tail light and headlight relays are the same. Check the numbers on them. This was even suggested in another thread though it was for a 2g.
     

    Street Build 225  3

    1991 Mitsubishi Eclipse N/T
    fwd · manual · 1G DSM
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  13. Cherry

    Cherry Proven Member

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    Oh, and another thing to look for which was brought up in that thread, look for wires being pinched by the pedals. Since there was rewiring this could be the case as well.
     

    Street Build 225  3

    1991 Mitsubishi Eclipse N/T
    fwd · manual · 1G DSM
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  14. sacrileger

    sacrileger Proven Member

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    i was thinking of doing exactly that and i do have another relay like that; however, i was not sure how it works and i did not want to damage the relay in case it was the short that took the relay and something else out... however, it appears the fuse gets blown out before the current gets to the relay so for that reason i did not explore this avenue too much...
     
  15. Cherry

    Cherry Proven Member

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    You could put the tail light relay into a working circuit like the headlight circuit. If the headlights work then the relay is good, if they dont then its bad.

    I would also think that they would act like the MPI relay but instead of the ECU pulling a certain pin or area to ground so the relay sends power to the right areas it is done by the switch. They most likely have constant power going to one pin on the relay, the switch pulls another pin to ground which allows the power to flow through the remaining pin to power what it needs to. Ill get out there tomorrow and test it. Might find out why all my lights just quit on me one night and I didnt want to mess around trying to find the problem.
     

    Street Build 225  3

    1991 Mitsubishi Eclipse N/T
    fwd · manual · 1G DSM
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  16. sacrileger

    sacrileger Proven Member

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    if you can test it that be great... at least the relays behaviour. i posted the circuit diagrams at the top of this thread:
    blowing 10Amp tail-light fuse

    the headlight relay is also used for the factory anti-theft system (shown in the diagram above). i can no longer figure out how mine (aftermarket) anti-theft was hooked into it. perhaps it was wired to the tail-light relay. there's really not that many components on the tail light circuit - dimmer, hazard, tail-lights, and...perhaps markers. i think the antitheft installer used the hazard switch for activating hazard and tails when triggered.
    i already spent so much time on this issue that i just need to know and find the problem just out of principle... the short must be some place b/w the dash and the relay.
     
  17. Cherry

    Cherry Proven Member

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    I did some research and it could be a lot of stuff. Could be a bulb shorting where the filaments touch and cause a short, pedals pinching the wires over time exposing the wire that creates a short to ground and that can blow a fuse, another the guys tire was rubbing on the front parking lights wiring which took the insulation off and they were shorting on each other which was blowing the fuse.

    There is another way you can tell if your relay is working, listen for the click. Its best if you have some help though. Turn the key to on and then turn the parking lights on and off, you should hear it click on and off. If it isnt doing that then it could be the switch is bad, the relay is bad, or some wires failed somewhere between the switch and the relay or the power going to the relay is bad. Let me go check to see if there is constant power going to a certain pin before I go and try setting my idle again. Had 2 wires crossed for the CTS that goes to the ECU so it wasnt getting any reading, the ECU kept thinking the engine was cold so it was trying to up the RPM but then it was conflicting with the RPM reading and creating a surge.Ill take some pictures so you can at least test the power pin if it has one. I could be completely wrong in how it works and im going off of how the MPI relay worked.
     

    Street Build 225  3

    1991 Mitsubishi Eclipse N/T
    fwd · manual · 1G DSM
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  18. sacrileger

    sacrileger Proven Member

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    thanks for the tip where to look for the el. short. i'll try all that this weekend... accept the relay. i'll have to bench test the relay once i find the step-by-step procedure since i get no power to the relay atm due to the blown fuse.

    btw, just a few weeks ago i was fighting CTS... crossed wires, faulty CTS, low voltage on ECU pin #20 which all together caused engine to misfire, running kinda funny, difficult to start etc. it's all documented here:
    Take a listen (video)... intermittent or persistent misfire?
     
  19. Cherry

    Cherry Proven Member

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    Alright. It might take a little while since I am eating lunch and im going show the flow on a picture I took with labels. But if your 10a tail light fuse is blowing then it has to be a short somewhere. If the 10a tail light fuse blows you get no power to the relay on pins 3 and 4 which are the 2 pins closest to the engine. Pin 2 is from the column switch which when that is triggered it sends power out of pin 1. If the fuse blows there is no power going to the relay.

    It looks like you just have to go through and check for shorts in the wires. Check the problem areas and then go from there. The other thing you could do is put a good 10a fuse in and then check pins 3 and 4 to see if you get power. If thats the case then I would definitely say there is a short to ground somewhere blowing the fuse.
     

    Street Build 225  3

    1991 Mitsubishi Eclipse N/T
    fwd · manual · 1G DSM
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  20. Cherry

    Cherry Proven Member

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    Well my dad likes to just overflow when putting water in the radiator, it would get on the connectors and it just ruined them. They literally crumbled away and a lot of the wire was bad which I cut out to good wire and replace it with new, when I rebuilt my engine and was putting the wires back on, since I dont have a connector though I found one that I just have to wire back in and im just going to redo what I did with solder, I put them in backwards and bam, idle surge. I was probably even tying to set the idle with them backwards and now my car stalls when it gets warm. Im going to reset the TPS since it is .16v off and then get it warmed up again, ground out the proper stuff and then reset the idle. Hopefully that will get everything sorted out then I can go from there.

    Also to test the relay I would think you would put power to pins 3 and 4, ground out pin 2 and then measure to see if you get power coming out of pin 1. The problem definitely sounds like a short somewhere though and you just have to find it. Who knows some mice could of gotten into that car at some point since it looks like it was sitting for a while and started chewing on random stuff exposing the wire causing a short which would blow the fuse.
     

    Street Build 225  3

    1991 Mitsubishi Eclipse N/T
    fwd · manual · 1G DSM
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  21. Cherry

    Cherry Proven Member

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    IMAG0322.jpg

    Here is the picture thats easier to read for the tail light relay. That is my understanding from looking at the wiring diagram and checking where constant power is showing when I measured them and combining the 2 just to make it a little more clear.

    I definitely need to clean my engine bay, thats just embarrassing.
     

    Street Build 225  3

    1991 Mitsubishi Eclipse N/T
    fwd · manual · 1G DSM
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    sacrileger likes this.
  22. sacrileger

    sacrileger Proven Member

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    great info.

    so I pulled the relay and checked for voltage on terminals which feed the relay and this is what i got:
    terminal #2 is always hot (12V)

    with the ignition key in ON position,
    terminal #1 and #2 is hot (12V)

    with the relay plugged in and the ignition key in ON position i get 12V on the load side of the 10A fuse. load side is the fuse terminal closer to the relay in your photo.

    no ignition key.. no voltage on the fuse terminals

    the way i checked for voltage is between the battery (+) and the fuse and relay terminals with the ground side of the voltmeter.

    so if i am reading this right.. i have a short some place on the column switch wire..., very likely under the dash, since i gather there should not be any voltage on relay terminal #2 with no key in ignition and no parasitic drain that i can detect.
     
  23. sacrileger

    sacrileger Proven Member

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    this test can be done without an assistant: i disconnected the (-) battery cable, turned the key to ON position and then listen for a "click" when connecting the (-) side to the battery terminal. my relay 'clicks' and i verified it is the tail light relay by keeping finger on the relay and 'feeling' the "click" on the outside casing.. .so the relay is good.
     
  24. Cherry

    Cherry Proven Member

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    I just used a test light. They are like 5-6 dollars at a parts store and are usually 12v test lights. Just hook it to ground and if something has power it lights up. Great for checking for power at fuses and things like that.

    From the wiring diagram terminals 3 and 4 should be constantly hot which is fed from the 10a fuse. Now in the wiring diagram I dont know if they are showing the relay, or where the relay plugs in, since it is a wiring diagram you would think it would be the wiring side and not the relay being shown. If its the relay being shown then I have 4&3 swapped and 2&1 swapped in my picture.

    From my understanding with a volt meter you want to have the ground on a ground, so battery - or body ground, and then you probe with the positive side of the volt meter to check for power and read voltages. Its the same way with a test light. The alligator clip side is the negative so that goes on any body ground or battery negative and the positive side is used for probing. You always, as far as I know, want to have the ground side of your test device connected to ground and then use the positive side to read the voltage of what you want to check, it looked like you were sending power from the battery + to what you were trying to test.
     

    Street Build 225  3

    1991 Mitsubishi Eclipse N/T
    fwd · manual · 1G DSM
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  25. sacrileger

    sacrileger Proven Member

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    i think this ^^^ method works when you have good circuit but should be reversed when you look for short. at least that was my understanding. i just tried to look it up and found this vid:
     
    Last edited: Jul 20, 2019

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