Is there information on fusible link wire that tells what the specific amp rating is per length and gauge of wire ?
For example : 5" of 16g fusible link wire is rated for ___ amps.
I searched 'fusible' and 'fusible link' and could not find anything specific.
The reason I am asking is that I would like to switch from fusible link wire to the cartridge style fusible links; the FLF/ PAL style .

Thanks Jeff

You might want to take a look at this page to find the per-foot resistance (in ohms) of wire by gauge size. Fuselink wire differs from regular wire in its insulation, not in its conductor, and is selected by sizing down by four relative to the gauge of the wire being protected. For example, a 12ga circuit is protected by a 16ga fuselink. You can take the gauge and length of your car's original fuselinks together with this chart's resistance information and use Ohm's Law to calculate a close approximation of the amperage protection value for any given fusible link, then round it to the nearest available plug-in type fuselink. Or, you can skip all that and simply read the "Upgrading the link" section of this page, which was written with '90s Mopars in mind, but the only real difference is that '90s Mopars have more fuselinks than your '75 did! This page talks about using Maxi fuses instead of the original wire-type fuselinks, and that certainly is one way to do it. Another way would be manual-reset circuit breakers, or cartridge-type fuselinks. When I have replaced fuselinks with fuses in the past, I've found it better to round slightly down rather than slightly up in selecting the fuse value, and — this is the important bit — specifically pick out a slow-acting fuse or breaker rather than a fast-acting one. This way, minor and unharmful transient current spikes won't kill the car dead, but a genuine overload condition will open the circuit.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Thanks Dan !!

As always your knowledge is amazing and most helpful.

Thanks Jeff

That was a fabulous link. I went back to home, and bookmarked the page. I am sure it will come in handy. Thank you.

Now, I still would like your recommendation for what size fuse to replace this link with. It seems as if it is the wire size of othewise unprotected wires under the dash that need to be taken into consideration. This entire design seems a little suspect to me.

On my '70 Dart, the yo-yo who had the car before me replaced the fusible link with plain wire. At some point he had run a screw through the steering column and shorted out the big red wire for the flasher circuit. His solutiion was to remove the flasher. That was most likely when he burned the fusable link. So, when I subsequently put a flasher in it, and tried the circuit, EL FLAMBEAU! But, it was the wiring harness under the dash that went up in flames. You never saw an old man move so fast in getting the battery unhooked,while smashing at burning wires with his bare hands.

This wire into the bulkhead connector carries power for most everything but the starter motor itself. It feeds the ammeter directly and everything goes on from there. The enigma here is that it seems like this should be a much bigger fuse than anything indicated in Mini Mopar's chart, but on the other hand it must protect a few more delicate, unfused circuits inside the dash. So too big doesn;t protect some circuits, and too small won;t handle the total power needed. What would be a better way to wire this?

I have decided to redo, pretty much in it's entirety, the wiring of this car. It is very hodge podge, and add on, not pretty, and probably not well designed at all. The dash harness likely will stay as it is, but the engine compartment wiring is up for redesign.

An Overview

As it stands, the key crank and run wires from the bulkhead connector are both hooked to a swtched fuse block that is on the drivers inner fender. All under hood things are run from there.

Many wires come back into the car from the inner fender fuse block to power add ons such as all the gauges, tachometer, knock gauge etc, and the after market AC. There is a second switched fuse block on the passenger inner fender fed by a long 12 gauge wire that runs around the front of the radiator. This fuse block serves all ECU related things such as fuel pump relay, and the ECU itself.

When I moved the battery to the trunk I brought both a hot and ground cable through the car and to stud bulkhead connectors under the dash. The first hot connection under the hood is to the starter motor, and then on to the solenoid. A Batt power fuse block is then feed from the solenoid on the inner fender, and from there on to the bulkhead connector. There is a 70 amp fuse between the starter solenoid and the batt power fuse block

I am not asking for a design of a wiring diagram. Any underlying principles, or maybe a link to a respected page on such things would be much appreciated. And lastly: what size fuse or resettable fuse should I put in that fusable link spot. The heaviest such resettable device that Cole Hersee lists is 30 Amps. They have bolt-in ones that are 50. I know I can get standard plug-in types at Advance Auto rated at 70A. I like the idea of getting the slow blow type, and the HC catalogue does not indicate that any of theirs are slow blow. Dan, is this company respectable? My local truckers supply company sells everything they list. I intend to draw a diagram of this new plan first, not only to check the logic of it, but to have something to refer to in the future, which I have never had before.

Thanks a bunch guys. I know this question blew all out of proportion to its original intent, but that's how my hobby projects seem to always go.

Sam

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H'mmm. I'm not sure how the amperage rating of a fabulous link is determined. It's hard enough determining the rating of a fusible link!
Well, the original idea behind the fusible link was "cost effective" circuit protection, which is a diplomatic way of saying cheap! Replacing a fuselink with a fuse is really kind of a moving target/best-educated-calculated-guess kind of situation. If you can try to closely calculate the maximum operating load of the circuit to be protected, and add a reasonable safety margin (not too large, not too small) you'll get close.
Sounds like a regular Silas Barnstable type! Did you find any of the fuses wrapped with tinfoil from chewing gum?
I can relate. I thought I must've told the story of when my father and I replaced the horn in his (now my) Lancer, but extensive searching fails to turn it up.

Dad wasn't into cars and didn't know much about how they worked, but we worked on the Lancer as a father-son type of thing. By and by, one of the car's two horns stopped working, so I grabbed one (sourced from a wrecking yard) off the garage shelf, tested it on the workbench with a reasonably well charged 12v battery, got some noise out of it, figured it was good, and dad and I proceeded to do the simple swap.

Once the "new" horn was in place and hooked up, dad put the battery cable back on the battery. I leaned in the passenger door and touched the horn ring. The new horn began to emit a squailng sound (kind of a mix of squawk, quack, and wail) which didn't stop when I jerked my hand away from the horn ring. After what could not have been more than one second, there was a giant puff of smoke, a loud frying sound, and the horn stopped making noise. All of this right in front of my completely stunned father and me. I scooted fast round to the battery and yanked the cable off, but I might as well have taken my time and stopped for a coffee on the way. The entire engine wiring harness was charcoal, burned beyond recognition — And it hadn't taken more than 2 or three seconds, though those two seconds went by in super slo-mo.

We stared at the smoke still curling up from the ruined wiring, and stared at each other, and stared back at the wiring, and back at each other. Obviously, the horn wasn't as good as I'd assumed based on my quickie bench test. I started apologising, but he waved it away and said "Dan, I think if you'd done something damn-fool, we'd both know it." It was just one of those things.

Of course, that still left us with a garage monument (non-running, non-driving car — and it was dad's only!) until it could be fixed. I was in high school at the time, so the next day on my lunch period I drove my '65 down to Santa Fe Blvd where there was a little-known wrecking yard, set back from the road and sunk down to a level well below it. I knew there was a '62 Valiant there (it contained one of four or five aluminum 225s around the Denver area that I kept meaning to go get and never did...). The yard was fully staffed with scary dogs and even scarier goons. I asked about the '62 Valiant and one of the goons chewed on his wodge of tobacco and said "I donno, twenny bucks for however much wiring you want out of it." Mmkay. Working quickly but carefully, I removed the engine wiring harness and a goodly portion of the dash harness, paid my $20, and gave the dogs wide berth on my way back to my Valiant.

On the way home from school that day, I stopped at a coin-op car wash, hung the engine harness on the wall by the floor mat clips, and powerwashed the grime off. It was in basically perfect condition...score!

That night, dad and I put in the "new" harness. It didn't take but about half an hour, working carefully; there aren't many wires on a '62 compared to later cars, but they're all important. The only wire we didn't connect was the one to the now-absent low-note horn.

That harness is still in the Lancer, but now it contains some main circuit protection (I don't recall what type or rating).

OK, enough reminiscing. You write:
Add individual protection for the small presently (almost said "currently") unfused circuits. The main circuit protection is a last-ditch safety device designed not to protect the branch circuits under it, but to prevent the car burning to the ground in the event of a major electrical catastrophe.

The main circuit protection therefore is properly selected as described above: Total up the maximum possible current through the circuit to be protected, making sure to include transient but normal conditions (such as extra current draw from the wiper motor when it's struggling against snow and ice), add a reasonable safety margin, and go from there. It's best to "split up" the safety margin. That is, don't just tack on more amps, but rather select a narrower safety margin and use a slow-blow circuit protection device (such as a fuselink or time-delay fuse or slow-acting circuit breaker). This way you allow safe transients without popping the protective device, but if there's a big, serious overload, the device will open the circuit.
Probably not a bad idea. Steer clear of the sadly-empty promises from the likes of "Painless" wiring.
A hodge podge Dodge bodge lodged in your garage?

Cole-Hersee are very reputable, as are Cutler-Hammer and Buss/Bussman and Littelfuse and various other makers of circuit protection and build devices. I just had a customer the other day point me at this nice-looking fuse block. Hella and Bosch also make very good relay blocks and boxes, fuse blocks and boxes, junction blocks and so forth.
Very good idea.
Always!

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Thanks Dan. And your story was interesting as well. In my situation, the burnt wiring harness led directly to the restoration of the car, which was fun, and very educational for me. It sounds to me like this situation you got caught in might have had a similar effect on your car skills; that of deepening, and broadening them. In fact your career now centers around automobile wires of one kind or another. I will go to the web sites you mentioned. Thanks.

Sam

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Dan, I did go to the web site and was happy with the neat electrical circuit stuff there. It is all for marine application, which means the stuff must be good quality to keep working in the the moist environment they are in. I found a local dealer, and will buy the fuse boxes, and such from them. Thanks for the tip. This is what makes this forum so great. I will look on the internet for any articles on automotive circuit design out there.
Sam

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Just FYI, I've found high current breakers, fuses, etc. at Waytek (www.waytekwire.com); I've been quite pleased with them.

Also, some fusible links use a special alloy or combinations of alloys for more precise control, although I've not seen that in a Mopar. I considered building a custom fusible link for the club Fury we're building, but it turns out the off-the-shelf solutions were good enough.

It seems to me there's a book out there on vehicular wiring. Maybe from HPbooks? Yeah, here it is . I haven't read it (at least not thoroughly, might've skimmed through it back when I was lucky enough to have a car-specific bookstore nearby in Denver). There's also this one which looks promising.

For my next trick, I will try to find an auto electrical book that I have read, many years ago, and found very helpful. This'll require a search of the Denver Public Library catalogue...

(time passes...)

I can't be 100% sure, but I am pretty certain it's this one. A quickie web search on the ISBN (ASIN) number shows you ought to be able to snag a copy for under $6.00 (though I also found one outfit asking over $150).

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Thanks Dan, I had found the HP book on line, and thought it too old, and maybe a little too elementary, with discussions of how electical motors work and such, so I was glad to see your link for the last one. I will order it today. I will delay any more silly questions until I have read it.

I went on line and found a chart of amp ratings for all wire gauges as well as a voltage drop calculator which was cool. But so far have not been able to find the power requirements of various standard automotive devices. That needs to be the next step in designing a wiring scheme.

Sam

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You don't want to use somebody's cookbook chart of "standard" (???) automotive device current draw. You want to measure. A clamp-type ammeter would be a very good investment...

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Do you check every device as you power it up? It seems like each device might be hard to isolate in the circuit. Here are some of the questions I need to answer, or at least would like to try and answer:
1. Draw from the ignition relay, and the solenoid. IE, the starting circuit minus the starter motor.
2. Ac clutch draw
3. Fan motor for AC blower.
4. Headlight relays, and Headlights them selves.
5. Fan motors.
ETC, ETC.

It would be nice to see how much power was required for a set of accesories, and then you would know what size wire to use for that branch of the circuit, and what size fuse to protect it. In thinking through this, it seems as if the fuses are more to keep the wire from carrying too heavy a load under short circuit situations, so you dont; burn you car down, rather than that of protecting your components, with the possible exception of the expensive things such as the ECU. Am I wrong about this? If this is true, then the fuse size is a function of what the wire can handle safely.

Then the guiding concern is what size wire is needed for the components being powered? I have always been a bigger is better kind of guy, but then it probably is better to actually know what is really required in a given circuit.

Here is a question, if you gang together 4 components which are supplied with #20 wire, such as dash meters, what size of single wire is required to handle the 4 #20's combined? Do you still fuse it to protect the smallest wire in the circuit? If you have a number #20 wire suppled by, say a number 16 earlier in the branch, then it seems as if the fuse would have to be a 10 amp fuse to blow before the # 20 wire started to cook. If the circuit branch started with a #16 feed, and you branched down to #20, the #16 would handle, in theory, 22 amps. But a 22 amp fuse would not blow soon enough to protect the #20 wire in the branch. So, do you never branch down to smaller wire in a circuit branch?

I said I wasn;t going to ask any silly questions until I got my book. I orderd the book this moring, but just couldn't help myself.

Sam

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You can do that, or you can put an ammeter in the main feed line and watch the reading as you add/subtract various devices.
Trivial. If you count this lot as 1 amp, you'll still be overestimating significantly.
Mmmm...specs should be in the service manual, or this'd be easy to measure.
Likewise easy to measure
Relays themselves draw almost no current. Lamp amperage can be obtained by dividing their nominal wattage by 13. You keeping those dim sealed beams, or going to put in something better?
Yep. Protecting the devices themselves is a secondary function, except, as you say, in case of e.g. computer modules.
Well...that's not really a reliable guideline, because wire size selection is not done strictly according to wire capacity. For one thing, the capacity of any given wire is contingent upon the acceptable voltage drop through the circuit (which in turn depends on what the circuit feeds and who gets to define "acceptable voltage drop"). Then you've got physical-strength requirements that might tend to call for a larger gauge of wire than is electrically necessary, and beancounters who often tend to call for a smaller gauge of wire than is electrically necessary.
It is difficult to go electrically wrong by using larger-than-required wire. The main concerns with larger wire are physical in nature (will the wire fit/can you get the appropriate terminal for the larger wire). It is easy to go electrically and mechanically wrong by using smaller-than-required wire. And keep in mind, not all wire is equal. For automotive service, you want stranded wire only, never household-type solid wire (which is not proof against the vibrations encountered in automotive service). Then there are different kinds of insulation depending on thermal and chemical proofing needs. If you want best-of-the-best, go search ebay for "silver teflon wire".
Excellent question, but it can only be answered with more questions. See above. What level of voltage drop is acceptable? Those four components, how much current do they draw, individually and together?
You fuse it according to the maximum operating current, not according to the wire size. Only fuselinks are selected according to wire size.
Happens all the time. It just has to be done correctly. Remember also that there are different kinds of overloads. Things like motors can draw variable current (including excessive current) due to operating conditions and electrical or mechanical faults, but things like light bulbs either draw the correct current or they dead-short. So max operating current is not always calculated the same way. And then there's strategic load calculation and fuse protection grouping. For example, protecting the dashboard lights and the brake lamps with the same fuse, so that if a brake light wire chafes on a metal edge and shorts, blowing the fuse, you'll suddenly have no dash lights and thus be made aware there's a problem. We havin' fun yet?

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

They say this type of mental exercise keeps you young. I don;t know how far back I want to go. I wll read the book. There is alot to know here. Thanks for your comments though. I hope to learn alot more, and am eager to do so.

Sam

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One thing you need to consider, is that Fans will draw much more current at start up, then when running at normal speed. Most OEM used fuse links in cooling fan circuits, before the use of PWM with built in current limiters.
I have seen cooling fans draw approx 50 amps at intial startup, and only about 10-15 amp running. What size fuse would you use for this? A fuse link will protect this circuit much better then a fuse.

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Charrlie_S
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