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Fusible link keeps melting/smoking??

Old 02-11-2015, 02:18 PM
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Fusible link keeps melting/smoking??

Hey all, first time poster. My 1977 280z blew a fusible link clean in half a few nights ago. Now, whenever I try to replace, the replacement keeps melting or smoking badly. I even unplugged the battery, then replaced the link, reattached the battery and still the link started to smoke badly. Any ideas?
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Old 02-11-2015, 03:07 PM
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You apparently have a short somewhere in your electrical system. Look for places where the insulation has worn off, possibly where a wire goes through a hole in the body. Fix that and you can replace the fusible link. That just shows that the link is working. It is a defense against shorts doing graver damage elsewhere in the car.
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Old 02-11-2015, 05:17 PM
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Hustlinghare is absolutely right.

Disconnect your battery. Then do what HH said and visually check all those places. If you can't visually find the problem, it gets tougher but think of it like a puzzle.

Now replace your fusible links and do not reconnect your battery.

Get yourself an ohmmeter and the electrical diagram for your car.

Do a test measurement between the battery cables to get a baseline reading. It should be pretty much ZERO. If it is not, you've got what I think is the worst, an intermittent short. That means jiggling things (wires, switches and so on) in the hopes of getting the short to show up.

You can then try disconnecting things and measuring the resistance between your two battery cables.

Don't bother disconnecting things which are protected by your regular fuses - if they were the problem, the fuses would have blown instead of your links.

Once you find the resistance goes up after a disconnection, that's likely to be the circuit with the problem and is where you need to inspect even more carefully.

When you do find the problem, don't just cover it with tape, try to figure out why it happened and see if there are any other places on your car which might do the same thing. Fix them in a way that prevents it from happening again.
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Old 02-12-2015, 12:22 PM
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Here's a trick if you don't have a multimeter. Hook up a 12 volt light to the hot feed side of the fuse tab and the other lead to a ground. It will stay lit until you find the source of the short without the danger.

Last edited by theramz; 02-12-2015 at 12:24 PM.
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Old 02-12-2015, 05:25 PM
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Originally Posted by theramz View Post
Here's a trick if you don't have a multimeter. Hook up a 12 volt light to the hot feed side of the fuse tab and the other lead to a ground. It will stay lit until you find the source of the short without the danger.
I love tricks! However, I don't quite understand this one. Could you elaborate a bit? Thanks!
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Old 02-12-2015, 06:05 PM
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Which fusible link blew? Take a wide enough picture that we can see where it is in the engine bay. That way, we might be able to narrow down your search.
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Old 02-12-2015, 06:21 PM
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By the way, did you do any work/modifications to the car before the link blew? I know someone who called me about a short after he put some flares on. I think he ran a screw into the body wiring harness.

Another off the wall possibility, is your alternator in good condition? If it shorts to ground, that could take out one of your links. Also of prime consideration are the ignition relay (I can build a replacement if it is bad.), ignition switch, steering column/combo switch, and going into the fuse box.
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Old 02-12-2015, 07:21 PM
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Originally Posted by beg3yrs View Post
I love tricks! However, I don't quite understand this one. Could you elaborate a bit? Thanks!
The two fuse pods each have two white/red wires going in and two going out. The light will only identfy the always hot side. Need more info on this post rather than show a noob how to possibly set his car on fire. The best thing is to visually check the harness. These wires feed to/from the alternator, ampmeter. fuse panel. Disconnect the neg battery cable and the big wire to the alternator. Replace the fuse link or hot wire it. Touch the neg cable to the battery. If you get a big spark it's not the alternator. A very small spark or none is normal and means the alt is bad.

Last edited by theramz; 02-12-2015 at 07:23 PM.
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Old 02-12-2015, 07:39 PM
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Originally Posted by theramz View Post
The two fuse pods each have two white/red wires going in and two going out. The light will only identfy the always hot side. Need more info on this post rather than show a noob how to possibly set his car on fire. The best thing is to visually check the harness. These wires feed to/from the alternator, ampmeter. fuse panel. Disconnect the neg battery cable and the big wire to the alternator. Replace the fuse link or hot wire it. Touch the neg cable to the battery. If you get a big spark it's not the alternator. A very small spark or none is normal and means the alt is bad.
Thanks! The voice of experience is something to which one should always listen...
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Old 02-12-2015, 08:40 PM
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The wire to the alternator could be shorted to ground. With battery hooked up and key off touch that wire to a ground source, youll know if you get a big spark it's the wire. You can use a similar test on other circuits. That main harness is tied down to the frame rail, a likely spot for a short.
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Old 02-27-2015, 08:17 PM
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Just happened to my '71 240Z. Turns out my alternator failed to dead short to ground. Replaced it and all is good.
datsun 240z alternator upgrade.
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Old 04-29-2015, 06:14 PM
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Originally Posted by beg3yrs View Post
Thanks! The voice of experience is something to which one should always listen...
Just remembered how you can do this safely. Disconnect the neg cable to the battery. Connect a test light to the neg side of the battery and the other end to body ground. if you indeed have a short the light will stay on untill you pull the right fuse or wire.
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