fuse problem

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Apr 3, 2008
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coarsegold, Ca
The 30 amp fuse that controls my head lights and control panle just randomly blew out. So I replaced it and it shortly blew out again. Then I tried a newer 30 amp fuse and that blew out also. I have been messing with this damn fuse for over a week and I can't figure it out. Does anyone know what I should do?:mad:
 

Poser

Oh...Durka Durka Durka.
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Welcome.


Start isolating things that are on that circuit.

Unplug the headlamp switch, the headlamps and the high-low beam switch, install the fuse and see what happens.


If the fuse does not blow, plug something back in until the fuse blows again.



After figuring out what you plug in and the fuse blows, you will need to figure out what is shorting to ground in those circuits.


:beer:
 
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The 1st thing I would do is check for continuity between the chassis (ground) and the load side of the fuse. If you get continuity, you have a short. You just need a $10 multimeter.
 
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The 1st thing I would do is check for continuity between the chassis (ground) and the load side of the fuse. If you get continuity, you have a short. You just need a $10 multimeter.

The way I see it is that it is not quite as simple as that. (As they say: "Life wasn't MEANT to be simple".)

You will get "continuity to earth" even if no short circuit is present (and the circuits are "normal") because your multimeter will send its current "through the bulbs to the earth" (in the same way that the battery does this when your lights are switched on).

But a multimeter should indeed show a "short-circuit" as "less resistance to earth than normal" which could be helpful (but of course THAT is not so easy to detect/identify as the difference between "no continuity" and "continuity").

The frame/bodywork of your wagon is all "earthed". (By that we mean "connected to the negative terminal of the battery".) So you are looking for somewhere where the + ve wiring AFTER THIS FUSE has found a "short-circuit to earth". Such places are commonly
  • Where part of the wiring loom has melted on part of the exhaust system
  • Where vibration has caused insulation on a wire to wear away so the wires inside touch bare metal
  • where someone has welded a panel unaware that wires were touching that panel on the other side
  • a collapsed taillight bulb fitting due to rust .....and so on
:cheers:
 
Joined
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You will get "continuity to earth" even if no short circuit is present (and the circuits are "normal") because your multimeter will send its current "through the bulbs to the earth" ...

I understand where you're comin from. From an engineering standpoint the lamps should conduct the signal from the multimeter right to ground/earth. But it doesn't on MY meter. Maybe my meter doesnt produce a large enough signal to run through a lamp to ground?
 
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I understand where you're comin from. From an engineering standpoint the lamps should conduct the signal from the multimeter right to ground/earth. But it doesn't on MY meter. Maybe my meter doesnt produce a large enough signal to run through a lamp to ground?


That's interesting.

I just went and got a spare brake/tail bulb and put MY multimeter across its filamants on its lowest-ohm setting (x1 setting). The "tail light filament" gives me "almost full-scale deflection" and the "brake light filament" gives me "full scale deflection".

(And of course the higher-ohm settings are worse. They give me "full scale" for both filaments.)

My meter is probably an ultra-ultra-cheapie though. I've never relied on it for accurate resistance readings.

I could try my cheap digital one but I can't see that working any better. And I haven't got the correct battery to put in my MONSTER multimeter in order to try that one.

I don't doubt what you say though - Because I know the filaments do indeed have resistance.
:cheers:
 

Colorado Boy-74-FJ40

I may grow older but I refuse to grow up!
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Mine had this same problem. Does it happen when you put in reverse by any chance? It took me a while to figure this out and discovered the reverse light got its power from the panel light circuit. I had a short-to-ground in the switch that screws into the transmission just behind the shifter (3 spd). It is a plunger switch that completes the hot circuit for the back up lights. It was grounding and blowing the fuse. It puzzled me for a while because it would work fine then I would notice that it was out not realizing that it was in conjunction with the reverse. oh well my .02
 
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coarsegold, Ca
No it it doesn't blow in reverse. It goes in about 15 sec after i switch the head lights/ gauges on. This is the first electricle work I have done on my fj40 and I am finding loose wires freaking everywhere.
 

steverb

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i was blowing headlight fuses. found out it was the connection going to the headlight. it was worn and loose causing it to heat up. so i cut them off and replaced with new. now i have no problems. also check the connections on the back of the fuse block same thing happens there.
 
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i was blowing headlight fuses. found out it was the connection going to the headlight. it was worn and loose causing it to heat up. so i cut them off and replaced with new. now i have no problems. also check the connections on the back of the fuse block same thing happens there.

Definitely check the back of the fuse block. For me the connector had actually melted to the fuse block which was causing me to blow fuses all the time when using my headlights. I couldn't figure out y, until i pulled the fuse block off and took a look.. thats when the "light bulb" went on... hahaha..
 
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First I would like to that everybody for there suggestions. Last night at about 2:00 am I finally figured it out. There were two wires in the switch that were loose and poorly connected. I removed them and cleaned the switch with some wd40 it worked like a charm. When my fuse didn't blow and smoke wasn't comming from my fuse box I shamlessly danced around my shop like a little girl. I wish it was as easy as it sounds but I spent hours removing and cleaning the fuse box and ground points not to mention hoplessly stairing at wires...The dishes are done dude.........
 
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i was blowing headlight fuses. found out it was the connection going to the headlight. it was worn and loose causing it to heat up. so i cut them off and replaced with new. now i have no problems. also check the connections on the back of the fuse block same thing happens there.
Where did you get new connections for the headlights?



Definitely check the back of the fuse block. For me the connector had actually melted to the fuse block which was causing me to blow fuses all the time when using my headlights. I couldn't figure out y, until i pulled the fuse block off and took a look.. thats when the "light bulb" went on... hahaha..
My fuse block has deformed because of my headlight fuse. I'm thinking about changing out all the wires to the headlight system except the high low beam stuff in the steering column. I've had problems turning on the headlights on my FJ40 since I got the thing. I'd have to wiggle the fuse everytime I wanted to use the headlights. So i'm going to run a single fuse beside the fuse box and leave the headlight fuse out of the fuse box. Everything else seems to work every time.
 
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Well I fixed my headlight fuse box problem. The headlight fuse got so hot it melted and deformed the bottom of my fuse box. When I cut the headlights on the fuse got hot quick. I guess it's high resistance and talking to a guy at work he said it has to be where the heat is, So unhooked the battery and pulled the fuse box. I cut the wires on both sides of that fuse and soldered on a separate fuse holder. Put everything back together and turned it on and have no heat at that new fuse. I now have a blank fuse holder on my OEM fuse block.
 
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Corrosion in the fuze holder will cause resistance in the fuze box - which heats up that thing and can cuase it to melt.

Pull the fuzes out, and use a little dowell with very fine sandpaper to clean the inside of the fuze holder contacts, if you feel any heat on your fuzes when electrical things are operating.

Headlights are the worst as they draw a lot of current.

Rocky
 

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