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1982 C/K 6.0L Caitlyn Mall Crawler (Interior time)

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How would I go about figuring out how to properly fuse my engine? On my ls swap I'm retaining the factory configuration of the battery to starter, then to the junction block. Also for the battery lug on the starter will run through the junction block.

Do I need fusible links on both wires? or is just the single wire from the starter to the block sufficient enough to protect the circuits? Isn't the cab protected by one also? What are the locations of the links and amps they are rated for?

The wiring diagrams are useless, they just say "fusible links"
Would getting it running and running a amp meter across each wire be my only solution to find the proper size fuse?
 
What sucks is the factory ones are long gone in the trash and the alternator puts out 80 more amps so I would think that would change it?
 
Starter cables in mine are not fused, using factory LS cables.

The cab has a fusible link on the end of each heavy gauge red wire coming from bulkhead (20amp), I shortened those to my liking and retained factory fusible links.

What I did to determine what size fuse to run in a circuit is to find the smallest wire in said circuit and run the size fuse closest to its maximum carrying capacity.
 
Babaganoosh said:
What sucks is the factory ones are long gone in the trash and the alternator puts out 80 more amps so I would think that would change it?
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I may be totally wrong here but as I understand it : a wire is only going to flow as many amps as it is capable of due to its size.

Increased alternator output won't automatically burn your wiring up, you just won't see potential increase in charging without upgrading wire size.
 
MAX89K5 said:
I may be totally wrong here but as I understand it : a wire is only going to flow as many amps as it is capable of due to its size.

Increased alternator output won't automatically burn your wiring up, you just won't see potential increase in charging without upgrading wire size.
Click to expand...

The alternator will still try to flow as much current as its regulator dictates (based on battery voltage). If the larger alternator thinks it needs the current, it will raise the voltage until it is satisfied with the voltage in the charging circuit. As it shoves more through the (presumably undersized) wires, they will heat up. With enough heat, an electrical fire will result. 100% chance.

I'm not saying that Baba is going to run into this problem, but I did want to point out the hazard of using your wire size as a current limiter. :doah:

Fuses are used to prevent this issue. By choosing a fuse of smaller capacity than your wiring, you guarantee that you'll never get into that situation.


Case in point - the PO of my Suburban wired up a "5 Amp" push button to power the 8 glow plugs directly, bypassing the relay. :doah: 60G glow plugs are rated for 15-20 amps apiece (depending on input voltage). The battery can't actually deliver that much current (the voltage drops quite a bit), but the amount is still larger than I have equipment to measure (ask me how I know :doah:). Running 8 plugs' worth of current through that tiny switch, his complaint was "it got real hot." :doah: :haha:

It worked (until it melted), but it was definitely a fire hazard. I would not have wanted to run that circuit for very many seconds.
 
You guys are correct on alternator output.

And to find the correct fuse for the wire I can ohm it.

Now the real question is what is fused under the hood?
 
Babaganoosh said:
How would I go about figuring out how to properly fuse my engine? On my ls swap I'm retaining the factory configuration of the battery to starter, then to the junction block. Also for the battery lug on the starter will run through the junction block.

Do I need fusible links on both wires? or is just the single wire from the starter to the block sufficient enough to protect the circuits? Isn't the cab protected by one also? What are the locations of the links and amps they are rated for?

The wiring diagrams are useless, they just say "fusible links"
Would getting it running and running a amp meter across each wire be my only solution to find the proper size fuse?
Click to expand...


I don't have answers for what values you should have, but you don't want to guess and check. That will only tell you how much current you are drawing. Which may have no relationship at all to how much you can safely draw.


Just to clarify, are you using your factory ('82) wiring with its fuses & wiring blocks, and then running the LS stuff off of one of the circuits on the old fuse block?
 
That makes perfect sense.

I would never rely on a charging wire of less than 8 GA. and expect it to work without burning.

I didn't mean to convey that if you use a 12 ga charging wire it would only flow 20 amps and there would be no issue. Not the case
 
MAX89K5 said:
That makes perfect sense.

I would never rely on a charging wire of less than 8 GA. and expect it to work without burning.

I didn't mean to convey that if you use a 12 ga charging wire it would only flow 20 amps and there would be no issue. Not the case
Click to expand...

Glad we're on the same page. :thumb:
 
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This is what is fused under my hood

Ignition 1 - coils, sensors 15 amp
Ignition 2 - injectors, trans. 15 amp
Fuel pump - 10 amp
PCM constant (org.) - 15amp
Speedometer - 5amp
High beam HID - 20amp
Low beam HID - 20amp
Cooling fan 1- 30amp
Cooling fan 2 - 30amp

5 relays, 2 for ignition, 2 for fans, 1 for fuel pump
 
Yes, my engine harness has the fuses already, I need it for the 1982 factory cab and for the alternator and powering the junction block on the firewall.

Sorry I wasn't to descriptive.
 
campfire said:
I don't have answers for what values you should have, but you don't want to guess and check. That will only tell you how much current you are drawing. Which may have no relationship at all to how much you can safely draw.


Just to clarify, are you using your factory ('82) wiring with its fuses & wiring blocks, and then running the LS stuff off of one of the circuits on the old fuse block?
Click to expand...

The ls engine harness is a stand alone with trans, it is all fused together. To make things easier and cleaner it is being powered off the junction block on the firewall.
 
I should have remembered you had a built harness, sorry for the clutter.

I have both heavy red wires from cab(with fusible link) running to the junction block on firewall along with a main power wire to power said block running to my underhood fuse box where it gets power. The other side of the junction block runs to HVAC.

All you have to do to provide power to the truck is to power those two heavy gauge red wires coming out of bulkhead connector in any way you would like.

As far as alternator wiring is concerned, it shouldn't be an issue. The factory LS battery cables have a 8ga leg that goes to the alternator.
 
The way I had planned to run the alternator was from the stud on the back to the junction block down to the starter like it was factory on this truck. The constant power needed in the engine harness will be ran off that same lug on the junction block.

My original engine harness was a hacked up mess so I literally cut it at the firewall bulkhead connector to solder and unhack it all.
 
I've never messed with fusible links. My understanding is you only use them when it's not possible to use a fuse. Here's a example of the info I've found:
A fusible link is not intended to be used in place of a fuse, only where a fuse cannot be used. When replacing fusible link, the wire gauge used should be 4 gauges smaller than the existing wiring circuit
Click to expand...

Mine an '89, but I'm pretty sure factory setup was alternator output to battery. Battery to starter and starter to the junction block/stud. Regardless of how the factory did it, that's how I have it now. Seems like it's a better setup to have the alternator run straight to the battery. I don't have a fuse in that feed. I haven't touched the factory wires that run from the starter so I don't know if they are fused or fusible link aside from the wiring diagrams saying they are.

If I were redoing it anyway, my preference would be to run a feed direct from the battery to the junction block/stud and skip the starter. Then put a fuse in the line. Trick will be figuring out what size fuse and gauge wire. The wire size is kinda easy because you can always go conservative and use over sized wiring. IMO a lot of the factory wiring seems to be undersized but maybe that's because they had better quality wire. If I read my '89 wiring diagram correctly, the wire from the junction block to the starter is 12ga or 8ga; the way those circuits are labeled isn't obvious to me which number is the wire size. So you're still stuck guessing at a fuse size. I would probably run a 150A fuse in that line.

Don't think I've been much help. Maybe you could junkyard source the wiring you had to remove so you're still using the factory stuff.
 
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