Upgrade from fusible links to circuit breakers

[FastWoman]

Hi all,

My fusible links are in horrible shape -- rotted, corroded, yet still conducting for the time being. Yeah, I know, replace them.

One of my fusible link assemblies has a broken base and is just dangling on the ends of the wires. Both covers are rotted. The only replacement items I'm finding are the covers. I'm sure I can find the wires too. perhaps a base at a junk yard. Even so, I wonder whether I shouldn't just replace the whole mess with something more practical.

I'm thinking of installing breakers like this:

http://www.wiringproducts.com/contents/en-us/d29.html

... or perhaps a very heavy duty fuse holder.

How do I find the amperage ratings on the fusible link wires? I have listed in the FSM that the black links are 1.25mm^2 (approx 16 ga), the green ones 0.5mm^2 (approx. 20 ga), and the brown ones 0.3mm^2 (approx. 25 ga). How do I find out at what ampacities these fusible links melt?

Also, has anyone replaced the fusible links with fuses or breakers? How well does this work.

Any thoughts about straying from OEM, even if it means an electrical upgrade?

Thanks for any input on this one!

Peace,

Sarah

[TomoHawk]

The best option seems to be the Maxifuse system

http://www.classiczcars.com/forums/showthread.php?t=18312

http://www.classiczcars.com/forums/showthread.php?t=17317

IMO, fuses are better to use, because they force you to investigate the cause, and curcuit breakers are better for things that may cause a momentary high-current situation, but not a serious fault.

There is a chart somewhere here showing the current ratings to subsitute fuse for the fusible links.

There's nothing wrong with the OE fusible links, a long as you keep it all in good condition, of course.

Edited August 23, 2009 by TomoHawk

[WingZr0]

The fuseable link covers from MSA are crap. Bought some about a year and half ago, drove 25 miles then parked at the race shop where it sat outside with the hood down. Went to look at the engine bay last month and noticed they were cracked, went to pick up one of them and it broke up like egg shells well as the other one. Granted i'm in NorCal and it's been 2 summers but what ever you do make sure those things are covered.

Edited August 23, 2009 by WingZr0

[sblake01]

The fuseable link covers from MSA are crap.

She won't need those covers if she's doing an upgrade to circuit breakers.

[FastWoman]

Thanks, TomoHawk! The maxifuses do look like a good possibility -- probably a lot cheaper than the breakers. I have SIX fusible links in my '78 -- four under cover and two in a double-connector clipped to the side of the relay housing cover.

Yeah, part of the motivation of the redesign is to get rid of the covers. I'm still wondering, though, whether I'll be hurting the value of the car by straying from the original design. My car is perhaps 99% stock. Even though it looks great, it's not a "show" car, and I intend to keep using it as a daily driver. Considering that, I think a small mod here or there isn't really going to hurt the value. Is my thinking correct here?

[sblake01]

I'm still wondering, though, whether I'll be hurting the value of the car by straying from the original design. My car is perhaps 99% stock. Even though it looks great, it's not a "show" car, and I intend to keep using it as a daily driver. Considering that, I think a small mod here or there isn't really going to hurt the value. Is my thinking correct here?

That pretty much describes the 280Z I recently sold. I had a rear spoiler, front air dam, window louvers, factory alloy wheels, a nice stereo system, etc. I made a profit on the sale based on what the car originally cost me, what I put in it and what I sold it for.

[FastWoman]

I'm still researching amperages. These links might be useful to someone:

http://whiteproducts.com/fusible-faqs.shtml

http://whiteproducts.com/fusible-specs.shtml

[FastWoman]

This is a nice little 4-gang distribution block:

http://www.darvex.net/Stinger-4-Gang-Gold-MAXI-0/M/B001IQIW78.htm?traffic_src=froogle&utm_medium=organic&utm_source=froogle

[FastWoman]

So all that's left is the ampacity of the lines. That's where it gets kinda weird.

Previous threads suggest the following values for the different links:

black (1.25mm^2, 16 ga) 80A

green (0.5mm^2, 20ga) 40A

brown (sometimes called "red", 0.3 mm^2, 25 ga) not mentioned

These links would ordinarily protect (by manufacturing convention) lines that are 4 gauge numbers larger in size...

black protects 12ga

green protects 16ga

brown protects 21ga

The AWG ratings for open air applications for these wire sizes are

12ga, 41A

16ga, 22A

21ga, 9A

Thus the ratings I've seen quoted here are about double the open-air ampacities of the lines they would supposedly be protecting. (I don't know the actual guage numbers of the wires used, though, without actually cutting them and measuring. Does anyone know what they are?)

The highest demand on any circuit would probably be from the alternator wire. I'm guessing that's protected with the black fusible link at supposedly 80A. I'm pretty sure the OEM alternator puts out 60A. Thus 80A seems a bit high from that standpoint too, but it also seems cranking 60A through a 12ga line is also a bit ambitious.

So I'm left wondering what the real ampacities of these circuits really are. Can anyone shed some light on this issue?

[TomoHawk]

I remembered where I saw a good write-up of the fusile link upgrade:

http://atlanticz.ca/zclub/techtips/fusiblelinks/index.html

[sblake01]

So I'm left wondering what the real ampacities of these circuits really are. Can anyone shed some light on this issue?

I'm thinking that back in the 70s things weren't quite as complicated as they are now and basically the fact that it worked the way Nissan set it up was all that really mattered. Didn't have to worry about things like "P0973-Shift Solenoid A Control Circuit Low" or "P0203-Injector Circuit Open Cylinder 3" back in those days so a little variance in ampacity rating wasn't too important.

[Langford Chuck]

Yes, I have been looking to upgrade my fuseblock/fusible links, in part to get rid of the fusible links, for the same reason you are: they are getting old and look unreliable to me. As well, though, I want to run some of my circuits (stereo, headlights, etc) through a new fuse block, on the basis that the 35 year old fuse box is surely approaching its limits.

The only thing about the maxi fuse is that it looks a little bling-like, and i was hoping for a clean but subdued look under my hood. As well, regular fuses are easier to find than maxi fuses, although i suppose you could just have a ready supply of them in the car for breakdowns.

But I am not finding many fuse boxes I like: I only want 6 or 4 circuits, i want it covered as it will be in the engine bay, and size should be on the compact side of things, which rules out most newer fuse boxes at the wrecker, which tend to have lots of breakers and relays and so are quite large. And, some of the aftermarket ones are pretty plain/crude looking. Once I locate a final one i will post the results, but would be happy to hear from others what they have used.