Look what I got away with - fusible link

[subzali]

So I think this is where a fusible link is supposed to go - between the battery and the wiring harness. Looks like the PO just connected the two wires together

Been 4 1/2 years that I've owned the truck and luckily no shorts

So is that the right diagnosis and is my local dealer the best place to get a replacement?

 

[Michael Hanson]

Yes. Mike

 

[ken_79-fj40]

I take it you read my thread about what can happen when you remove the fusible links? I'm off to go pick up another harness in a few minutes.

 

[subzali]

yes and that was very timely considering I had never thought of looking to see if I still had a fusible link or not - bummer about your harness, but look on the bright side - you saved mine

 

[wbb72fj40]

Yeah ken your a real wire saver with your post. My P.O. strait wire it also, so I am picking one up today.

Good ole ken savin wiring harnesses everywhere (well except his own)

 

[fjnutter]

Is a fuseable link a requirement or can one use an inline blade type fuse harness?


Nut

 

[subzali]

I also have a couple questions about the fusible link:

-What would cause the fusible link to fry?
-How would I tell if the fusible link is fried? The ammeter normally reads around "0" when the battery is charged, which would also be the case of the fusible link is fried. Does the engine not run if the link is fried?

Looking at the wiring diagram, it is connected to the ammeter, and from there to the positive terminal of the alternator, which then goes to fused connections. So it doesn't protect against any fused circuit from shorting, does it blow if the alternator dies so there's a large drain on the battery?

 

[numby]

-What would cause the fusible link to fry?
-How would I tell if the fusible link is fried? The ammeter normally reads around "0" when the battery is charged, which would also be the case of the fusible link is fried. Does the engine not run if the link is fried?

Looking at the wiring diagram, it is connected to the ammeter, and from there to the positive terminal of the alternator, which then goes to fused connections. So it doesn't protect against any fused circuit from shorting, does it blow if the alternator dies so there's a large drain on the battery?

The few burned out fusible links that I've found on Toyota vehicles stopped them dead in their tracks.

The link is connected to the battery at the positive lug. If it burns out then no current should get past that point into the system.

And for fjnutter...

No you can't safely use a blade fuse in place of a fusible link. Conventional fuses prevent sudden shorts, etc. A fusible link is designed to burn out during low level problems that would not "blow a fuse" but slowly burn out your entire wiring system.

 

[JB740i]

Does the maxifuse on my american autowire harness perform the same function?

 

[ken_79-fj40]

I actually used a length of GM 14 gauge fusible link wire to replace the one on the harness I got. I dissasembled the factory plugs , cleaned up the terminals, and re-used them with the GM wire. When I first bought my truck the fusible links went up in smoke when the same power lead that just wrecked my harness shorted out on something. I had thought about using inline fuses instead, but a few others I spoke with locally didn't think it was a good idea. Considering how much time and money I spent installing the new harness (which is working perfectly by the way) I took their advice and used a fusible link.

 

[FishNinJay]

hmm.. I only have 1 fat wire off my POS.. going to the starter. I'll dig deeper and see if there is a hot line going from the starter to the fuses and look for a fusible link. Lately, I've been doing some fuel line and carb work, so this would be a particularly bad time to have a wiring disaster!

 

[Pin_Head]

So I think this is where a fusible link is supposed to go - between the battery and the wiring harness. Looks like the PO just connected the two wires together

The wire with the yellow butt splice appears to be the original fusible link that burned out once and was repaired by splicing. The other wires at the battery are not fused.

 

[MoCoNative]

So what size fusible link is required here?

I went with an inline glass fuse, as my thinking was that was replaceable in the field, and you have spares on board for a 40. I think I used a 20 amp fuse or so. But now you guys have me worried that I should go back to a fusible link wire.

 

[subzali]

So can someone explain to me why the truck will not run if/when the fusible link is gone? The positive side of the battery is (indirectly) connected to the wiring circuits for the truck, but the positive side of the alternator is too. So won't the alternator just keep the truck running?

 

[ken_79-fj40]

Nope it won't. Pinhead will probably correct me if i'm wrong but it seems like if the fusible links go out the alternator will no longer be connected to the rest of the wiring harness. When the fusible link goes, the only place power can go from the battery is straight to the starter, but with no power to the rest of the truck the ignition key wouldn't do anything either.

 

[numby]

Correct AFAIK. The battery to starter cable remains functional but there's no way to power the solenoid without a fusible link. If you have a wire running direct from the alternator to the battery then it's most likely an alteration. I think Mark at MadElectric does this sort of thing. Been in his shop a number of times back in them olden days - he's a bright fellow.

 

[subzali]

My interpretation of the Wiring Diagram is that the alternator is connected directly to the rest of the wiring harness, and only connected to the battery through the ammeter and fusible link. But does the battery somehow act as a "pulsation" sink like the bottle on an air compressor, capturing the "pulses" of current/voltage from the alternator?

So if my fusible link burns up, what is the process of finding where there is a defective wire/wires? Is it only above the fuse block (because the fuses protect the rest of the circuits)? Or do I have to test each circuit in order to find where the fault is?

 

[fjnutter]

Did a search online and saw this little write up.Catalog
Sounds like to me that the link is saving the main power lead feeding the dash from completely burning up.With the link at the battery you pretty much lose the fuselink wire and thats about it(hopefully).
Also, noted 2 things in the write up
1-don't install fuselinks inside the cab
2-the fuselink wire gauge needs to be 2 gauges smaller than the wire it connects to



nutt

 

[numby]

My interpretation of the Wiring Diagram is that the alternator is connected directly to the rest of the wiring harness, and only connected to the battery through the ammeter and fusible link.

I think that's basically right. Everything is downstream from the ammeter.

There is also an old error in the factory '78 wiring diagram. The L/R line labeled ACC on the ignition switch should read ST - or START - and the small B/W line should be labeled ACC instead of ST. Note that it runs directly to the radio. Sorry - neither here nor there but it used to bug me.

So if my fusible link burns up, what is the process of finding where there is a defective wire/wires? Is it only above the fuse block (because the fuses protect the rest of the circuits)? Or do I have to test each circuit in order to find where the fault is?

I'd have the alternator and voltage regulator checked first and proceed from there. Those are the first major draws/feeds on the system.

 

[numby]

So is that the right diagnosis and is my local dealer the best place to get a replacement?

subzali - It's possible that what occurred with your vehicle was that the fusible link burned out at some point in the past. Then the the previous owner cut off the offending fried portion and spliced the white wire on to connect to the battery. I think you may still have a small portion of link wire remaining. The factory link is a short (3-4") piece of black wire with large white connectors on either end. The remaining white wire that's coming from your battery positive normally has a matching large black connector like what's on the other side.

My truck had no fusible link when I got it but I figured it out within a month or so which clued me in to these things a bit. I got a replacement (and new factory positive cable) at the dealer.

The few vehicles I've encountered with burned out links were simply stopped and couldn't be started. There's no solenoid click when the key is turned even if the battery is new. Never asked if the vehicles died while driving. I just reached in and felt the fusible link wire and it would have a break in it. The link wires looked as if they had gotten hot but there was only one small break.

I wonder if you could've push started the stranded vehicles?