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Marios280Z

Recommendation for new radiator and elctrical fan for 280Z

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That fuse must have been defective or of poor design or both.  A proper fuse of that design typically fails with absolutely no drama.  Most people don't even realize it's blown unless they inspect it closely.  No smoke, smell, heat, or burn marks.  Just a missing filament.

 

And many amps through a dead short will melt the wire insulation.  You'll get smoke and smell then.  I would check the wire on the back of the fuse box that attach to that fuse terminal.  It's probably melty looking.  Follow it up in to the harness and you might find the short.  It's probably waiting for the right bump.

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 I would check the wire on the back of the fuse box that attach to that fuse terminal.  It's probably melty looking.  Follow it up in to the harness and you might find the short.  It's probably waiting for the right bump.

 

Will do.

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Well the biggest bummer right now is that if the problem spontaneously went away, you can be sure that it will spontaneously come back again.

 

Are you double dog sure it doesn't have anything to do with the electrical work you just did? You were messing around up front near the parking lights with the fan install. I know it's unlikely, but just seems too coincidental.

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Last night I pulled out the fuse box to take a closer look at the wires coming into i. NONE of them looked like there was any type of failure. All good, not burned isolation, nothing. Chased it as far as I could to where it went into harness, and I still couldn't find anything. 

Considering how hot the fuse burned down, is it possible that the shortage took place somewhere else down the harness other than fuse itself? I was expecting to find melted wire at least in the vicinity of that fuse.

 

 

Well the biggest bummer right now is that if the problem spontaneously went away, you can be sure that it will spontaneously come back again.

 

Are you double dog sure it doesn't have anything to do with the electrical work you just did? You were messing around up front near the parking lights with the fan install. I know it's unlikely, but just seems too coincidental.

 

I agree...I hate those problems that are not repeatable. 

I'm quite confident that I did NOT brake anything wiring wise when  I was installing fans. I cannot, however, speak for what effect the fans have on the electrical system. Like I mentioned before, I did not notice a whole lot more load on the system, gauging by the dash volt meter.  The only thing right now that is questionable regarding the fan harness is the manual override wire which suppose to be connected to manual switch that is in turn connected to 12 V low amperage signal. At this point the wire is sitting coiled together in the engine bay. There is a possibility that the wire might have touched the body of the car effectively grounding it. I have hard time believing that this would create the issue, since the wire goes back to the fans relay. 

 

I'm still planning to look at all the other lights connected to that harness.

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Regarding the override wire shorting to ground in the engine bay, I don't think that would cause the issue you had, but it could be a problem.

 

If you've got it wired as shown in the instruction sheet and the ignition switch is on, when the temp switch closes, you've got +12 on the yellow wire. And since the yellow and greens are tied together at the module, you've got +12 on the green. Shorting the green to ground would be a connection to ground through the ignition and temp switches.

 

Also, a little unrelated, but just noticed that they have a diode on the override wire. I'd put it on the one coming from the ignition switch instead. The way they have it, you can't back power the override source from the ignition, but I think it would be more important to make sure that you can't back power the ignition from the override source. Especially if the override source is hot at all times. Did I say that right?  Does that make sense?  :)

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Considering how hot the fuse burned down, is it possible that the shortage took place somewhere else down the harness other than fuse itself? I was expecting to find melted wire at least in the vicinity of that fuse.

 

And yes, it's completely conceivable that whatever shorted was far from the fuse block. For brief periods of time, copper wires can carry an enormous amount of current. Even the smaller ones.

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Regarding the override wire shorting to ground in the engine bay, I don't think that would cause the issue you had, but it could be a problem.

 

If you've got it wired as shown in the instruction sheet and the ignition switch is on, when the temp switch closes, you've got +12 on the yellow wire. And since the yellow and greens are tied together at the module, you've got +12 on the green. Shorting the green to ground would be a connection to ground through the ignition and temp switches.

 

 Wouldn't the diode on the green wire (override) prevent from grounding path?

 

 

Also, a little unrelated, but just noticed that they have a diode on the override wire. I'd put it on the one coming from the ignition switch instead. The way they have it, you can't back power the override source from the ignition, but I think it would be more important to make sure that you can't back power the ignition from the override source. Especially if the override source is hot at all times. Did I say that right?  Does that make sense?  :)

 I think I got it. You recommend to put a diode, which is directional, on the yellow wire in a way that would allow flow from the temp sensor back to relay, but not the other way around, correct?

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Yes, if you've got the diode on the green, then it should protect against a grounding path. That's not what it's for, but it will do that as well.

 

Actually the best thing would be to have diodes on both wires feeding that relay. Diode OR them together such that either of them could feed the relay without affecting the other.

 

 

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I wonder if a bad fuse alone could cause the melting and self-destruction.  No short involved, just the fuse developing resistance at a bad junction and building heat from normal current flow.  Might be searching for a phantom.

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Hey guys, just want to say that I finally wired the manual can override. I used one of the rubber grommets as rozzi sugested to bring the wire into the cabin. Then I repurposed the REAR DEFOGER switch and connected the wire from my can relay to it as seen in the picture.

post-30354-0-10194600-1446342110_thumb.j

The black wire is the one that I brought from the relay. The fan instal manual shows to use 15A fuse inline with the hot wire going into the switch, and since the DEFOGER has its own 20A fuse in the fuse box, I think I'm OK. Just to be clear my DEFOGER does not work. I get the power at the REAR window, but unfortunately all the traces are broken. So I thought it was a good use of a currently installed switch. I also get nice blue light indication telling me that the fan is on. If any of you sees anything wrong with this implementation, let me know.

On a different note, I have not investigate the REAR lights any further to look for a potential short. I've been driving for a while now and everything seems to be OK. I'm really wondering if it was a case of a 38 year old fuse that simply failed.

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