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Correct Fusible Link?


Spawn

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Well, I lost complete electrical to the truck while I was driving (headlights, stereo, everything).  I have been searching through the forums and online and I've gotten some decent ideas, but my biggest issue is figuring out the correct sizing/amperage rating for making (or possibly buying) a new fusible link for my '77 620.  I'm not sure if replacing the L20b with a KA24DE would have any impact on the sizing/amperage rating, but we never changed out the old fusible link that was being used with the L20b and it was working fine.  Unfortunately, with age and the NE environment, the connection corroded and broke near one of the crimped positions.  I ended up trying to simply patch in a wire to get the truck back up and running, but it eventually ended up not surviving as you can see below.  (The yellow circles were the position that I repaired after the fusible link had broken - as a bonus you can see where the small fire, that most likely resulted from the wire probably overheating, caused the crimped bullet connectors I used to melt)

Aztgycm.jpg

Using Cardinal Grammeter's comment about http://www.vintageconnections.com in another fusible link post, I was able to find the connectors circled in red (or at least some connectors that are very similar), but I want to make sure that I size the fusible link wire correctly.  The downside is that I don't have enough of the fusible link wire to be able to read the wire gauge on it, and I don't know/trust if the color of it is green, grey or black, and I have read that the color determined the amperage rating.

I have also read that the fusible link wire should be about 5.5" to 6" long (from the http://www.madelectrical.com/catalog/fusible-link.shtml page), so I'm thinking that if I can determine the correct fusible link wire gauge that I will make it 6" long and put one of each of the connectors on the opposing ends so that I can have a cable coming off of the positive terminal with a connector on it and then just insert the fusible link with a connector on either end so that no tools will be needed to swap out the fusible link in the event it goes out.

So hopefully if you've read this far you may happen to have a 1977 620 wiring diagram that might happen to indicate the gauge size of the fusible link, or maybe even the amperage that was going through that wire?  I suspect that most likely this wire feeds the fuse block, alternator or starter, due to the fact that with it not being connected there is absolutely no power to the vehicle (although I didn't try the hazard lights).

Thanks in advance for any help you can provide to figure out this little puzzle!

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The 620 should be using a GREEN code fusible link rated at 40 amp continuous and capable of 200 amp for 5 seconds.

 

Engine size doesn't matter. The total load on the system (lights, heater, wipers etc) would. The fusible link must allow for all the electrical draw but melt through in the event of a catastrophic short to ground like in an accident. 

 

The fusible link is insulated with Hypalon and special plastic that is fire resistant. For that reason, never wrap a fusible link with electrical tape. 

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Thanks, Datzenmike!  I'll see if NAPA or AutoZone may happen to have the fusible link wire in green, rated for 40A. (hopefully, someone knows the proper wire gauge size or I can figure it out as I'm sure this will be more what they use).  The fusible link was not wrapped with electrical tape, that dark portion that looks like vinyl electrical tape is actually the charred remnants of the crimped on bullet connectors!

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I just looked on NAPA online and see that they have 14, 16, 18 & 20 ga. primary wire fusible link.  None of them are green, so I'm not sure if I should go with the smallest (20 ga.) or a larger size.  Datzenmike, do you happen to know what the wire gauge size is for the OEM green fusible link?

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1 hour ago, banzai510(hainz) said:

I would think 20 ga is to small.  20 ga is not going to power the whole car with Lights on!!!!!!!!!!!!!!!!!!!!!!!!!!

 

what happens usually is the link weakens and ehen you load it down it will melt, most likely at the crimped end where loose strainds are then it pops say when you hit the high beams(happen to me)  I just recrimpedit and its been fine.

I went to NAPA and they had a set of calipers there that we used to measure the remaining wire portion of the fusible link. It measured just a touch under 1.00mm in diameter for the copper portion.  That indicated that it was either an 18 ga. (0.8mm) or 16 ga. (1.0mm) so I went with the 16 gauge.  Unfortunately, they didn't have any of the connectors, so I'm going to order some of them online to build a few proper link lengths (handy to have a couple of spares just in case).  Until the connectors come in, I'm just going to splice the remaining old portion in with a length of the new wire and then replace it when the connectors arrive.  Their website said they ship on Tuesday, Thursday & Friday, and take up to 4 days for shipping in the USA, so hopefully, the package will ship out today and I can expect to see them by Saturday or maybe Monday.

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The Green is 0.52mm or 20 gauge wire. 16 gauge would handle about 60 amps.

 

96c928c4-1478-46d4-934f-f24c49205de8.png

 

  • 20 gauge: 0.5 square mm
  • 18 gauge: 0.8 square mm 
  • 16 gauge: 1.0 square mm
  • 14 gauge: 2.0 square mm

 

Your protection is 40 amps. More than this and you risk your wire harness in the event of a really bad short to ground. It's there to blow just like it's name... fusible link.

 

 

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So you're saying that I would be better off getting 20 gauge to be safe?  I just wish that the industry stuck with standard color coding for the gauges and the amperage rating, then it would be very easy to ensure that you get the right fusible link.

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On 11/16/2018 at 11:00 AM, ]2eDeYe said:

Newer cars use main fuses. 

I am running a stock size fusible link with my KA and haven't had any issues.  
 

 

What's the stock size you're using Redeye?  Is it a 20 gauge?

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I didn't even notice I didn't have a fusible link on my 72' 620 until I saw this thread, previous owner apparently got rid of it for straight 12 gauge wire. 20 gauge does seem really small but I'm assuming that's the size I should install even though I don't know if the original one was green or not. I picked up a full 50ft roll of 20g fusible link wire to make a few, if anyone can't find 20g let me know and I'll send you some for postage. I'm never going to use all of it.

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On 11/17/2018 at 3:19 PM, Spawn said:

What's the stock size you're using Redeye?  Is it a 20 gauge?

 

On 11/17/2018 at 4:12 PM, datzenmike said:

Nissan uses a color code. If it's green then yes.

 

I don't remember, you can strip a piece off whats left of your stock wire and match them up.

 

Looks green in your pic :) 

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2 hours ago, distributorguy said:

Its not original, but this circuit breaker will solve your problem, and you can reset it if it pops.

https://www.amazon.com/Jili-Online-Waterproof-Circuit-Breaker/dp/B072WR2SKM

 

The fusible link will handle hundreds of amps for a short time without blowing..... you know, like when you put a wrench down on the battery? 20 gauge seems kind of small but it works. Again this will probably never be needed but it might.

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4 hours ago, datzenmike said:

 

The fusible link will handle hundreds of amps for a short time without blowing..... you know, like when you put a wrench down on the battery? 20 gauge seems kind of small but it works. Again this will probably never be needed but it might.

 

I can confirm the size on my 72, most had been cut off but I found a short section of the original green fusible link still attached when I replaced mine, and the copper wire itself (not the coating) was actually a tiny bit smaller than the new 20g fusible link wire I bought when I measured it. 20g seems small for sure but works absolutely fine for me. 

Edited by damesta
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On 11/19/2018 at 7:48 AM, distributorguy said:

Its not original, but this circuit breaker will solve your problem, and you can reset it if it pops.

https://www.amazon.com/Jili-Online-Waterproof-Circuit-Breaker/dp/B072WR2SKM

 

I'm guessing for this, I would just use regular wire to feed the input and output and then mount on the fender or somewhere inside the engine bay.  Has anyone actually used this item?

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3 hours ago, Spawn said:

 

I'm guessing for this, I would just use regular wire to feed the input and output and then mount on the fender or somewhere inside the engine bay.  Has anyone actually used this item?

 

Correct, probably 12ish gauge wire. Downside is it can be tripped a lot easier than a fusible link can be blown. As Mike has said several times, the fusible link wire can handle a few hundred amps for a few seconds, the circuit breaker will trip as soon as anything over 40 amps hits it. Sure you can pull over and reset it real quick, but it may do it relatively often depending on your setup. Fusible link still gets my vote..but fuses or circuit breakers will definitely work. Pick your poison.

Edited by damesta
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You would put this near the fuse panel, possibly within reach from the driver's seat.  There is no single circuit in your truck that would draw close to 40A, so its a safe assumption to say it should never need resetting unless you have a dead short or a mis-wired circuit.  I haven't used this specific one, but have used others.  Fusible links are an archaic way of protecting a circuit, like using fuses in your home instead of circuit breakers.  

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The problem with putting inside the cab and away from the battery is you are removing it's intended use. The wire from the battery to the fuse is unprotected. Even a fender bender may pinch and ground it and it will heat up like a toaster. Last thing you want under the hood near gas and what about the rest of your wire harness getting melted. This is why the fusible links are connected directly to the battery positive post or close by.

 

Make a mount close to the battery that is easy to see and get at and have several extra fuses there also so they are easy to find and change in the dark. Unlikely though it might be.

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  • 3 years later...

I used to be amazed how many times a fusible like would jump out of a 620 into the bottom of my tool box at the Pick 'n Pull. Haha But no more. I think there had only been one 620 in the PDX yards in the last three years. The Ratsun Bros picked that sucker clean in hours.

 

While I was pulling service on something I stress the crip connectors to one of the plugs and it broke. My spares don't really look any better...

 

Why can't I get a new fusible link and crimp nice connectors? Make a better part. Counter guy at Napa couldn't come up with any reference to fusible links and there wasn't anything generic in blister packs. Struck out at Baxter's/Auto Zone, O'Reily's because they all source the same catalogs. 

 

I can't believe it. I do a Google search; Repalcement for fusible link. Bang... NAPA online:

 

Primary Wire Fusible Link 14 ga.     Part #: BEL 784696     Line: Belden

Primary Wire Fusible Link 16 ga.      Part #: BEL 78469     Line: Belden

 

But no amperage listed for the part, It's just a short piece of wire and an eyelet. They are five or six bucks.

 

Here is from Advanced Auto Parts online:

 

This part Dorman - Conduct-Tite 14 Gauge Fusible Link Wire         Part No. 85620 is rated at 30 amps.

 

This part Dorman - Conduct-Tite 16 Gauge GM Fusible Link           Part # 85621 is rated for 20 amps.

 

A little more money for Dorman brand, about six or seven bucks.

 

 
 
 
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The counter guys are hamstrung by not being able to search the web. No internet access on the job is what I was told by my local branch manager. So when I see a counter guy struggling to come up with something in their computer system or antiquated books, I'll bust out my phone and search online, and I usually come up with a part number faster than they can.

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  • 4 months later...
On 11/13/2018 at 6:11 AM, datzenmike said:

The 620 should be using a GREEN code fusible link rated at 40 amp continuous and capable of 200 amp for 5 seconds.

 

Engine size doesn't matter. The total load on the system (lights, heater, wipers etc) would. The fusible link must allow for all the electrical draw but melt through in the event of a catastrophic short to ground like in an accident. 

 

The fusible link is insulated with Hypalon and special plastic that is fire resistant. For that reason, never wrap a fusible link with electrical tape. 

 

Would a fuse-holding wire with a 40amp fuse plugged in do the trick?

 

10 Gauge Fuse Holder - 10 AWG Inline Fuse Holder with 40 AMP ATC Blade Fuses (4pack) https://a.co/d/j7yl346

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