280Z fusible links

[Captain Obvious]

21 hours ago, wal280z said:

The brown fusible links were replaced by 30A Maxi-fuses.

Why? Fusible link "D" has the most draw on the right-hand side of the fuse-block inside the cabin. It hasn't blown. I didn't want to start high and end up melting the inside fuse-block.

The alternator output is at an 80A maxi-fuse. My memory is going to the crapper and that crapper is flushed multiple times a day, but, if I recall correctly, I found a internally regulated 65A alternator from a early 80's Maxima in the junkyard. There's a 60A Maxi-fuse, and there's an 80A Maxi-fuse. Which would you choose?

Fuses and other protective devices are not a field of expertise I've been even grazed by in my travels as an EE. But I can tell you that even though the whole thing sounds so simple and mundane, I highly suspect the experts in the field would be quick to refute that. In other words... I bet the people who really know what they're talking about in this facet of engineering (which isn't me) would be able to debate the finer points of this for hours.

That said... I took a quick look on the web and came to the following conclusions:

1.25 mm sq is approx. the same as 16 ga
0.3  mm sq is approx the same as 22 ga   32 ga

And also with some web searching, it seems that the "general convention" seems to be that the fusible link gauge should be four sizes smaller than the wires they are intended to protect. So, for example, 12 ga. wire should be protected by a 16 ga. fusible link. And 18 ga. wire should be protected by a 22 ga. fusible link.

All that really makes me wonder if that brown 0.3 mm sq link is really really correct. Maybe that red link really was the correct one all along?

Edited March 16, 2019 by Captain Obvious
Slipped a decimal point

[Zed Head]

40 minutes ago, Captain Obvious said:

All that really makes me wonder if that brown 0.3 mm sq link is really really correct. Maybe that red link really was the correct one all along?

Wouldn't you need to know what the smallest gauge is among all of the circuits on that link?

I've wondered about Nissan making a mistake but it seems unlikely that they would repeat it year after year, through various FSM's, as other links change size along the way.  Like from 76 to 77.  They changed a green 0.5 to a brown 0.3.  Somebody had to have done some calculations there.

Maybe the red came from somebody else second-guessing the engineers?  But if 0.3 hasn't been melting, what reason would you have to go to 0.5?  Extra risk for no benefit.

[Captain Obvious]

11 hours ago, Zed Head said:

Wouldn't you need to know what the smallest gauge is among all of the circuits on that link?

I've wondered about Nissan making a mistake but it seems unlikely that they would repeat it year after year

Well I'm pretty sure there isn't any 28 Ga wiring anywhere in the infrastructure. There might be some stuff that small as it enters components (like solenoids and the like), but I don't think actual wire in any harness is that small.

In any event what you said about the 0.3... "if 0.3 hasn't been melting, what reason would you have to go to 0.5?" echoes exactly my note above when I said "anecdotally that the brand new 0.3 "sorta brown, sorta tan, sorta salmon" links I have installed run nice and cool. Implication being that they are large enough."

So I agree... Why argue with success, right? Put the smallest, easiest to blow protective device in there that still allows the system to operate properly. The only thing I DON'T know is if I have ever operated my system under peak load. By that, I mean... I've never run the HVAC fan on full blast at night with the high beams on, while running the rear defrost, wipers, and hitting the brakes on a hot summer night while running the A/C and having the flashers on.

Probably never will.

[Captain Obvious]

So for some additional info, I couldn't stand it anymore so I started playing around with some of the on-line translators. Everyone likes info, right? Here's a probably correct interpretation of most of the pertinent info on those Yazaki fusible link data sheets:

The only thing I can't figure out is exactly what is the difference between the FLWX and the FTX series. It clearly has something to do with tin-dipping. My guess is that the FTX series uses smaller individual strands and then they tin dip the strands a second time once they are wound together. Might make them more accurate or have a sharper melt characteristic?

Anyway, here's some datasheets. FTX (this is where the 0.3 brown comes from):

And the FLWX  (this is where the 1.25 black link comes from):

[Zed Head]

I got the impression that they were localizing the melting to a small specific spot, instead of the whole wire, for FTX over FLWX.  Based on your translation.

I wonder if a good meter could distinguish between red and brown links.  They supply resistance numbers.

Here's what Nissan wrote in 1976 with their Service Bulleting about changes.

 

[SteveJ]

You would have to have a sensitive meter to measure the resistance. While the red link should have about half of the resistance of the brown, the contact of the meter leads on the ends of the fusible links would probably create more resistance.. Here are the AWG approximations of the different fusible link sizes along with the resistance of those wires in milliohm/foot.

	AWG	mm^2	mOhm/ft
Black	16	1.31	4.016
Red	19	0.65	8.051
Brown	22	0.33	16.14

[Captain Obvious]

Thanks Steve. You just pointed out that I slipped a decimal point in one of my earlier comparisons. I had said that .3 was similar to 32 ga, but it's not. That would be .03, not .3

Wonder if it's too late to edit my previous incorrect info...   Not too late. Fixed it.

[Captain Obvious]

2 hours ago, Zed Head said:

I got the impression that they were localizing the melting to a small specific spot, instead of the whole wire, for FTX over FLWX.  Based on your translation.

I wonder if a good meter could distinguish between red and brown links.  They supply resistance numbers.

I got the same impression about the melting spot as you did, but here's the rub... They clearly do the tin dip before they put the insulation on. And Yazaki don't know how long the end user is going to cut the length of wire. So if they are tin dipping just in select spots, they won't know where that dipped spot will end up (or how many will end up) in the finished product. I think the dip has to apply to the entire length.

And as for measuring the resistance difference between the red and the brown, I don't have a meter anywhere near that good. Probably easiest to push an accurately known "highish" current through it and measure the voltage.

But I gotta ask.... Why would you need to resort to measuring the resistance when you can just look at the jacket color or measure the diameter of the conductor with calipers? Based on the thicker insulation of the old style red links, I suspect they are the FLWX 0.85.

[Captain Obvious]

Zed Head, Forgot... I also saw the notes about the fusible links in the 76 TSB as well. I went digging in there to see what I could find about the changes.

I really think the snippet you posted does a really good job of showing the function of the links:
 

2 hours ago, Zed Head said:

 

 

 

[Zed Head]

13 minutes ago, Captain Obvious said:

But I gotta ask.... Why would you need to resort to measuring the resistance when you can just look at the jacket color or measure the diameter of the conductor with calipers? Based on the thicker insulation of the old style red links, I suspect they are the FLWX 0.85.

Really just want to know where MSA and others get their red links, and what I have on mine.  I don't know if I have 0.69 new red or 0.3 old red, or if new red is 0.3 after all.  A test for other people would be nice too.  Plus, sometimes I test things even though they're not a problem.  I can't easily get to the conductor to measure it with the fittings on the end.  

Surprised that the MSA guys didn't reply.  They've been around, on the Koni strut thread.

[wal280z]

On 3/13/2019 at 11:39 AM, Captain Obvious said:

Yes, I do believe the mis-placement did carry over from 77 into the 78 year. I think the location of the biggest (black) link never changed. I think they got it right on the diagram in 76 (right front), and then screwed it up in 77 which carried into 78.

Not to beat a dead horse, but I got a hair up my asre'y and decided to look up what Nissan published in the fiche... Same error of misplacement on the location of the fusible links...

Maybe Nissan had it right (in the design), and the (unknown) manufacturer of the wiring harness had a oops moment.... for all of the whole production  year(s).... how DEEP shall we DIG.....

 

[Zed Head]

Looks like they also got their numbers backward.  Three 1.25 links (key 5), and one 0.3 (key 6).